Intercell interference coordination accounting for machine type communication

ABSTRACT

A method of operating a base station in a wireless telecommunications system. Downlink communications from the base station to terminal devices are made using a plurality of OFDM sub-carriers spanning a system frequency bandwidth. The base station supports communications with a first type of terminal device on a host carrier using OFDM sub-carriers distributed across the system frequency bandwidth and supports communications with a second type of terminal device on a restricted bandwidth carrier using OFDM subcarriers distributed across a restricted frequency bandwidth which is smaller than and within the system frequency bandwidth. Respective base stations can exchange information regarding their restricted bandwidth carrier transmissions to help them coordinate their respective transmissions with a view to reducing intercell interference.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a divisional of U.S. patent application Ser.No. 14/650,991 filed Jun. 10, 2015, which is based on PCT ApplicationPCT/GB2014/050077 filed Jan. 13, 2014, and claims priority to BritishPatent Application 1300770.3 filed in the UK IPO on Jan. 16, 2013, theentire contents of each of which being incorporated herein by reference.

BACKGROUND OF THE INVENTION

The present invention relates to methods and apparatus for use inwireless (mobile) telecommunications systems. In particular, embodimentsof the invention relate to interference considerations intelecommunications systems.

Third and fourth generation mobile telecommunication systems, such asthose based on the 3GPP defined UMTS and Long Term Evolution (LTE)architecture are able to support more sophisticated services than simplevoice and messaging services offered by previous generations of mobiletelecommunication systems.

For example, with the improved radio interface and enhanced data ratesprovided by LTE systems, a user is able to enjoy high data rateapplications such as mobile video streaming and mobile videoconferencing that would previously only have been available via a fixedline data connection. The demand to deploy third and fourth generationnetworks is therefore strong and the coverage area of these networks,i.e. locations where access to the networks is possible, is expected toincrease rapidly.

The anticipated widespread deployment of third and fourth generationnetworks has led to the parallel development of a class of devices andapplications which, rather than taking advantage of the high data ratesavailable, instead take advantage of the robust radio interface andincreasing ubiquity of the coverage area. Examples include so-calledmachine type communication (MTC) applications, which are typified bysemi-autonomous or autonomous wireless communication devices (i.e. MTCdevices) communicating small amounts of data on a relatively infrequentbasis. Examples include so-called smart meters which, for example, arelocated in a customer's house and periodically transmit information backto a central MTC server relating to the customers consumption of autility such as gas, water, electricity and so on. Further informationon characteristics of MTC-type devices can be found, for example, in thecorresponding standards, such as ETSI TS 122 368 V10.530 (2011July)/3GPP TS 22.368 version 10.5.0 Release 10) [1]. Some typicalcharacteristics of MTC type terminal devices/MTC type data mightinclude, for example, characteristics such as low mobility, high delaytolerance, small data transmissions, infrequent transmission andgroup-based features, policing and addressing.

Whilst it can be convenient for a terminal such as an MTC type terminalto take advantage of the wide coverage area provided by a third orfourth generation mobile telecommunication network there are at presentdisadvantages. Unlike a conventional third or fourth generation terminaldevice such as a smartphone, an MTC-type terminal is preferablyrelatively simple and inexpensive and able to operate on relatively lowresources (e.g. low power consumption). The type of functions performedby the MTC-type terminal (e.g. collecting and reporting back data) donot require particularly complex processing to perform, and furthermoreare typically not time-critical. However, third and fourth generationmobile telecommunication networks typically employ advanced datamodulation techniques on the radio interface which can be power hungryand require more complex and expensive radio transceivers to implement.It is usually justified to include such complex transceivers in asmartphone as a smartphone will typically require a powerful processorto perform typical smartphone type functions. However, as indicatedabove, there is now a desire to use relatively inexpensive and lesscomplex devices able to operate with low resource usage to communicateusing LTE type networks. To this end, so-called “virtual carriers” havebeen proposed and some characteristics of these are discussed furtherbelow.

The increasingly widespread deployment of wireless telecommunicationssystems can give rise to more likelihood of interference betweenneighbouring cells. This is particularly the case for LTE based systemswhich generally adopt a unit frequency reuse approach in whichneighbouring cells employ the same radio frequencies. This means aterminal device at a boundary between two communication cells can bereceiving comparable signal levels from different base stations usingthe same frequency resources, thereby leading to potentially significantinterference. There have been proposals to address such intercellinterference in LTE-type networks using what are generally referred toas Intercell Interference Coordination (ICIC) techniques.

One ICIC technique is the so-called soft frequency reuse approach. Inaccordance with this technique a base station allocates resources todifferent terminal devices using different frequencies depending on therespective terminal devices' geographic locations. In particular,neighbouring base stations coordinate so that at geographic locations inthe vicinity of boundaries between two communication cells (coverageareas) associated with two base stations, one of the base stationscommunicates with its connected terminal devices in one frequency band,whilst the other base station communicates with its connected terminaldevices in a different frequency band. Thus, in accordance with thisapproach, a terminal device near a boundary between two cells andconnected to a first base station is less prone to interference from aneighbouring base station because the neighbouring base station will beusing a different frequency band to serve its connected terminal devicesin the vicinity of the cell boundary at that location. Each base stationmay communicate with terminal devices away from cell boundaries (e.g. atcell centre) using all frequencies, with such transmissions typicallybeing made at a lower power than for transmissions associated withterminal devices in the vicinity of the cell edge.

Another ICIC technique has been proposed for telecommunications networksincluding a macro base station serving an area that includes one or morefemto- or pico-cells (served by respective femto- or pico-basestations). This technique uses so-called Almost Blank Subframes. Inaccordance with this approach, the base station will select subframes inwhich it will make almost no transmissions (for example retaining onlycell reference signals) and will communicate the timings of these“almost blank subframes” to network elements supporting communicationsin the femto- or pico-cells. Communications within the femto-/pico-cellscan then be coordinated to occur during the subframes in which the macrobase station is transmitting an almost blank subframe, thereby reducingthe potential for the macro base station to interfere withcommunications in the femto-/pico-cells.

More details on ICIC techniques, such as those described above, can befound in a paper published by Nomor Research GmbH—“Heterogeneous LTENetworks and Intercell Interference Coordination” by Pauli et al. andalso from an article published by ZTE Corporation—“Enhanced ICIC forLTE-A HetNet” by Xiong. Details regarding the protocols for coordinatingcommunications between base stations, for example on the X2 interface ofan LTE network, can be found in the relevant standards, for example inETSI TS 136 420 V11.0.0 (2012-10)/3GPP TS 36.420 version 11.0.0 (Release11) [15] and 3GPP TS 36.423 version 11.2.0 (Release 11) [16].

The present inventors have recognised how the proposed introduction ofvirtual carriers in wireless telecommunications systems may give rise toadditional intercell interference considerations that should beaddressed to optimise communications in such systems. For example, it isfrequently proposed that virtual carriers may be particularly useful forsupporting machine type communication devices and the inventors haverecognised that such devices may frequently be located in areas ofrelatively poor network coverage, i.e. they may be “hard to reach”devices. For example, smart-meter type MTC devices might often belocated in a basement or other location with relatively high penetrationloss. This can mean high transmission powers may often be required tosupport reliable communications on virtual carriers, thereby giving riseto additional intercell interference concerns.

There is therefore a desire to provide wireless telecommunicationsapparatus and methods which are able to further help supportcommunications with terminal devices with reduced intercellinterference.

SUMMARY OF THE INVENTION

According to a first aspect of the invention there is provided a methodof operating a base station in a wireless telecommunications system inwhich downlink communications from the base station to terminal devicesare made using a plurality of Orthogonal Frequency Division Multiplex,OFDM, sub-carriers spanning a system frequency bandwidth, and whereinthe base station supports communications with a first type of terminaldevice on a host carrier using OFDM sub-carriers distributed across thesystem frequency bandwidth and supports communications with a secondtype of terminal device on a restricted bandwidth carrier using OFDMsub-carriers distributed across a restricted frequency bandwidth,wherein the restricted frequency bandwidth is smaller than and withinthe system frequency bandwidth, and wherein the method comprises:selecting a transmission characteristic for transmissions to be made bythe base station to the second type of terminal device using therestricted bandwidth carrier; and conveying an indication of thetransmission characteristic from the base station to at least one otherbase station of the wireless telecommunications system.

In accordance with some embodiments the transmission characteristiccomprises frequency and/or time resources on which transmissions are tobe made by the base station to the second type of terminal device usingthe restricted bandwidth carrier.

In accordance with some embodiments the indication of the transmissioncharacteristic comprises an identifier for a range of frequencies forthe restricted bandwidth carrier selected from a set of potential rangesof frequencies for restricted bandwidth carriers that the base stationis able to support.

In accordance with some embodiments the indication of the transmissioncharacteristic comprises an indication of physical resource blocks to beused by the base station for transmitting the restricted bandwidthcarrier.

In accordance with some embodiments the indication of the transmissioncharacteristic comprises an indication that transmissions are to be madeby the base station to the second type of terminal device using therestricted bandwidth carrier with a maximum transmission power thresholdwhich is greater than a maximum transmission power threshold forcontemporaneous transmissions to be made by the base station to thefirst type of terminal device using the host carrier.

In accordance with some embodiments the wireless telecommunicationssystem uses a radio frame structure comprising subframes, and whereinthe indication of the transmission characteristic comprises anindication of one or more subframes to be used by the base station fortransmissions to the second type of terminal device using the restrictedbandwidth carrier.

In accordance with some embodiments the method further comprisesreceiving from a further base station of the wireless telecommunicationssystem an indication of a transmission characteristic to be used by thefurther base station for transmissions to the second type of terminaldevice using a reduced bandwidth carrier, and taking account of theindication of the transmission characteristic received from the furtherbase station when selecting the transmission characteristic fortransmissions to be made by the base station using the restrictedbandwidth carrier.

In accordance with some embodiments the indication of a transmissioncharacteristic received from the further base station comprises anindication of frequency and/or time resources on which transmissions areto be made by the further base station to the second type of terminaldevice using a restricted bandwidth carrier associated with the furtherbase station, and wherein the step of selecting a transmissioncharacteristic for transmissions to be made by the base station to thesecond type of terminal device using the restricted bandwidth carriercomprises selecting frequency and/or time resources to be used for therestricted bandwidth carrier which are different from the frequencyand/or time resources comprising the indication of a transmissioncharacteristic received from the further base station.

In accordance with some embodiments the further base station from whichan indication of frequency and/or time resources on which transmissionsare to be made by the further base station is received is one of the atleast one other base station to which the base station conveys its ownindication of a transmission characteristic.

In accordance with some embodiments the indication of the transmissioncharacteristic is conveyed from the base station to the at least oneother base station of the wireless telecommunications system over apoint-to-point logical interface between the base station and respectiveones of the at least one other base station.

In accordance with some embodiments the indication of the transmissioncharacteristic is conveyed from the base station to the at least oneother base station of the wireless telecommunications system over an X2interface of the wireless telecommunications system.

In accordance with some embodiments the indication of the transmissioncharacteristic is conveyed to the at least one other base station in aninformation element defined for the X2 interface.

In accordance with some embodiments the method further comprises makingtransmissions to the second type of terminal device in accordance withthe selected transmission characteristic using the restricted bandwidthcarrier with a maximum transmission power threshold which is greaterthan a maximum transmission power threshold for contemporaneoustransmissions made by the base station to the first type of terminaldevice using the host carrier.

In accordance with some embodiments the method further comprises makingtransmissions to the second type of terminal device in accordance withthe selected transmission characteristic using the restricted bandwidthcarrier with a transmission power which is greater than a maximumtransmission power threshold for contemporaneous transmissions made bythe base station to the first type of terminal device using the hostcarrier.

In accordance with some embodiments the first type of terminal deviceand the second type of terminal device are types of terminal devicehaving different operating capabilities.

According to another aspect of the invention there is provided a basestation in a wireless telecommunications system in which downlinkcommunications from the base station to terminal devices are made usinga plurality of Orthogonal Frequency Division Multiplex, OFDM,sub-carriers spanning a system frequency bandwidth, and wherein the basestation supports communications with a first type of terminal device ona host carrier using OFDM sub-carriers distributed across the systemfrequency bandwidth and supports communications with a second type ofterminal device on a restricted bandwidth carrier using OFDMsub-carriers distributed across a restricted frequency bandwidth,wherein the restricted frequency bandwidth is smaller than and withinthe system frequency bandwidth, and wherein the method comprises:wherein the base station is configured to select a transmissioncharacteristic for transmissions to be made by the base station to thesecond type of terminal device using the restricted bandwidth carrierand convey an indication of the transmission characteristic to at leastone other base station of the wireless telecommunications system.

According to another aspect of the invention there is provided a methodof operating a base station in a wireless telecommunications system inwhich downlink communications from the base station to terminal devicesare made using a plurality of Orthogonal Frequency Division Multiplex,OFDM, sub-carriers spanning a system frequency bandwidth, and whereinthe base station supports communications with a first type of terminaldevice on a host carrier using OFDM sub-carriers distributed across thesystem frequency bandwidth and supports communications with a secondtype of terminal device on a restricted bandwidth carrier using OFDMsub-carriers distributed across a restricted frequency bandwidth,wherein the restricted frequency bandwidth is smaller than and withinthe system frequency bandwidth, and wherein the method comprises:receiving from a further base station of the wireless telecommunicationssystem an indication of a transmission characteristic to be used by thefurther base station for transmissions to the second type of terminaldevice using a reduced bandwidth carrier associated with the furtherbase station; and selecting a transmission characteristic fortransmissions to be made by the base station to the second type ofterminal device using the restricted bandwidth carrier in a manner thattakes account of the indication of the transmission characteristicreceived from the further base station.

In accordance with some embodiments the transmission characteristicassociated with the indication received from the further base stationcomprises frequency and/or time resources on which transmissions are tobe made by the further base station to the second type of terminaldevice using a restricted bandwidth carrier.

In accordance with some embodiments the transmission characteristicassociated with the indication received from the further base stationcomprises an identifier for a range of frequencies for the restrictedbandwidth carrier selected from a set of potential ranges of frequenciesfor restricted bandwidth carriers that are supported in the wirelesstelecommunications system.

In accordance with some embodiments the transmission characteristicassociated with the indication received from the further base stationcomprises an indication of physical resource blocks to be used by thefurther base station for transmitting a restricted bandwidth carrier.

In accordance with some embodiments the wireless telecommunicationssystem uses a radio frame structure comprising subframes, and whereinthe indication of the transmission characteristic received from thefurther base station comprises an indication of one or more subframes tobe used by the further base station for transmissions to the second typeof terminal device using a restricted bandwidth carrier.

In accordance with some embodiments the indication received from thefurther base station comprises an indication that transmissions are tobe made by the further base station to the second type of terminaldevice using a restricted bandwidth carrier with a maximum transmissionpower threshold which is greater than a maximum transmission powerthreshold for contemporaneous transmissions to be made by the furtherbase station to the first type of terminal device.

In accordance with some embodiments the transmission characteristicselected by the base station for transmissions to be made to the secondtype of terminal device using the restricted bandwidth carrier comprisesfrequency and/or time resources on which the transmissions are to bemade by the base station to the second type of terminal device using therestricted bandwidth carrier.

In accordance with some embodiments the indication of a transmissioncharacteristic received from the further base station comprises anindication of frequency and/or time resources on which transmissions areto be made by the further base station to the second type of terminaldevice using a restricted bandwidth carrier associated with the furtherbase station, and wherein the step of selecting a transmissioncharacteristic for transmissions to be made by the base station to thesecond type of terminal device using the restricted bandwidth carriercomprises selecting frequency and/or time resources to be used for therestricted bandwidth carrier which are different from the frequencyand/or time resources comprising the indication of a transmissioncharacteristic received from the further base station.

In accordance with some embodiments the method further comprisesconveying an indication of the transmission characteristic selected bythe base station for transmissions to be made by the base station to thesecond type of terminal device using the restricted bandwidth carrier toat least one other base station of the wireless telecommunicationssystem.

In accordance with some embodiments the further base station from whichan indication of frequency and/or time resources on which transmissionsare to be made by the further base station is received is one of the atleast one other base station to which the base station conveys anindication of the selected transmission characteristic.

In accordance with some embodiments the method further comprises makingtransmissions to the second type of terminal device in accordance withthe selected transmission characteristic using the restricted bandwidthcarrier with a maximum transmission power threshold which is greaterthan a maximum transmission power threshold for contemporaneoustransmissions made by the base station to the first type of terminaldevice using the host carrier.

In accordance with some embodiments the method further comprises makingtransmissions to the second type of terminal device in accordance withthe selected transmission characteristic using the restricted bandwidthcarrier with a transmission power which is greater than a maximumtransmission power threshold for contemporaneous transmissions made bythe base station to the first type of terminal device using the hostcarrier.

In accordance with some embodiments the indication of the transmissioncharacteristic is received from the further base station over apoint-to-point logical interface between the base station and thefurther base station.

In accordance with some embodiments the indication of the transmissioncharacteristic is received from the further base station over an X2interface of the wireless telecommunications system.

In accordance with some embodiments the indication of the transmissioncharacteristic is received from the further base station in aninformation element defined for the X2 interface.

In accordance with some embodiments the first type of terminal deviceand the second type of terminal device are types of terminal devicehaving different operating capabilities.

According to another aspect of the invention there is provided a basestation in a wireless telecommunications system in which downlinkcommunications from the base station to terminal devices are made usinga plurality of Orthogonal Frequency Division Multiplex, OFDM,sub-carriers spanning a system frequency bandwidth, and wherein the basestation supports communications with a first type of terminal device ona host carrier using OFDM sub-carriers distributed across the systemfrequency bandwidth and supports communications with a second type ofterminal device on a restricted bandwidth carrier using OFDMsub-carriers distributed across a restricted frequency bandwidth,wherein the restricted frequency bandwidth is smaller than and withinthe system frequency bandwidth, and wherein the base station isconfigured to receive from a further base station of the wirelesstelecommunications system an indication of a transmission characteristicto be used by the further base station for transmissions to the secondtype of terminal device using a reduced bandwidth carrier associatedwith the further base station; and to select a transmissioncharacteristic for transmissions to be made by the base station to thesecond type of terminal device using the restricted bandwidth carrier ina manner that takes account of the indication of the transmissioncharacteristic received from the further base station.

It will be appreciated that features and aspects of the inventiondescribed above in relation to the first and other aspects of theinvention are equally applicable to, and may be combined with,embodiments of the invention according to other aspects of the inventionas appropriate, and not just in the specific combinations describedabove.

BRIEF DESCRIPTION OF DRAWINGS

Embodiments of the present invention will now be described by way ofexample only with reference to the accompanying drawings where likeparts are provided with corresponding reference numerals and in which:

FIG. 1 provides a schematic diagram illustrating an example of aconventional mobile telecommunication network;

FIG. 2 provides a schematic diagram illustrating a conventional LTEradio frame;

FIG. 3 provides a schematic diagram illustrating an example of aconventional LTE downlink radio subframe;

FIG. 4 provides a schematic diagram illustrating a conventional LTE“camp-on” procedure;

FIG. 5 provides a schematic diagram illustrating an LTE downlink radiosubframe in which a virtual carrier has been inserted in accordance withan embodiment of the invention;

FIG. 6 provides a schematic diagram illustrating an adapted LTE“camp-on” procedure for camping on to a virtual carrier;

FIG. 7 provides a schematic diagram illustrating LTE downlink radiosubframes in accordance with an embodiment of the present invention;

FIG. 8 provides a schematic diagram illustrating a physical broadcastchannel (PBCH);

FIG. 9 provides a schematic diagram illustrating an LTE downlink radiosubframe in accordance with an embodiment of the present invention;

FIG. 10 provides a schematic diagram illustrating an LTE downlink radiosubframe in which a virtual carrier has been inserted in accordance withan embodiment of the invention;

FIGS. 11A to 11D provide schematic diagrams illustrating positioning oflocation signals within a LTE downlink subframe according to embodimentsof the present invention;

FIG. 12 provides a schematic diagram illustrating a group of subframesin which two virtual carriers change location within a host carrier bandaccording to an embodiment of the present invention;

FIGS. 13A to 13C provide schematic diagrams illustrating LTE uplinksubframes in which an uplink virtual carrier has been inserted inaccordance with an embodiment of the present invention;

FIG. 14 provides a schematic diagram showing part of an adapted LTEmobile telecommunication network arranged in accordance with an exampleof the present invention;

FIG. 15 schematically represents a maximum allowed transmission power asa function of frequency in a conventional wireless telecommunicationssystem providing support for a virtual carrier as previously proposed(left-hand side of the figure) and in a wireless telecommunicationssystem providing support for a virtual carrier in accordance with anembodiment of the invention (right-hand side of the figure);

FIG. 16 is a signalling ladder diagram representing coordination amongbase stations with regards to virtual carrier transmissions inaccordance with an embodiment of the invention.

FIG. 17 schematically represents respective transmissions from two basestations in accordance with an embodiment of invention (top row in thefigure) and the corresponding combined signal that might be seen by aterminal device in the vicinity of a boundary between the cellssupported by the respective base stations (lower part in the figure);

FIG. 18 is a flowchart schematically representing operating steps of abase station in accordance with an embodiment of the invention;

FIGS. 19 to 22 are signalling ladder diagrams schematically representingsome example approaches for establishing whether a terminal device mightbenefit from power boosted virtual carrier operation in accordance withan embodiment of the invention.

DESCRIPTION OF EXAMPLE EMBODIMENTS

Embodiments of the invention may in particular be employed within thecontext of what might be termed “virtual carriers” operating within abandwidth of a “host carriers”. The concepts of virtual carriers aredescribed in co-pending UK patent applications numbered GB 1101970.0[2], GB 1101981.7 [3], GB 1101966.8 [4], GB 1101983.3 [5], GB 1101853.8[6], GB 1101982.5 [7], GB 1101980.9 [8], GB 1101972.6 [9], GB 1121767.6[10] and GB 1121766.8 [11] the contents of which are incorporated hereinby reference. The reader is referred to these co-pending applicationsfor more details, but for ease of reference an overview of the conceptof virtual carriers is also provided here.

Conventional Network

FIG. 1 provides a schematic diagram illustrating some basicfunctionality of a wireless telecommunications network/system 100operating in accordance with LTE principles. Various elements of FIG. 1and their respective modes of operation are well-known and defined inthe relevant standards administered by the 3GPP® body and also describedin many books on the subject, for example, Holma H. and Toskala A [12].

The network includes a plurality of base stations 101 connected to acore network 102. Each base station provides a coverage area 103 (i.e. acell) within which data can be communicated to and from terminal devices104. Data is transmitted from base stations 101 to terminal devices 104within their respective coverage areas 103 via a radio downlink. Data istransmitted from terminal devices 104 to the base stations 101 via aradio uplink. The core network 102 routes data to and from the terminaldevices 104 via the respective base stations 101 and provides functionssuch as authentication, mobility management, charging and so on.

Mobile telecommunications systems such as those arranged in accordancewith the 3GPP defined Long Term Evolution (LTE) architecture use anorthogonal frequency division multiplex (OFDM) based interface for theradio downlink (so-called OFDMA) and the radio uplink (so-calledSC-FDMA). FIG. 2 shows a schematic diagram illustrating an OFDM basedLTE downlink radio frame 201. The LTE downlink radio frame istransmitted from an LTE base station (known as an enhanced Node B) andlasts 10 ms. The downlink radio frame comprises ten subframes, eachsubframe lasting 1 ms. A primary synchronisation signal (PSS) and asecondary synchronisation signal (SSS) are transmitted in the first andsixth subframes of the LTE frame. A primary broadcast channel (PBCH) istransmitted in the first subframe of the LTE frame. The PSS, SSS andPBCH are discussed in more detail below.

FIG. 3 is a schematic diagram of a grid which illustrates the structureof an example conventional downlink LTE subframe. The subframe comprisesa predetermined number of symbols which are transmitted over a 1 msperiod. Each symbol comprises a predetermined number of orthogonalsub-carriers distributed across the bandwidth of the downlink radiocarrier.

The example subframe shown in FIG. 3 comprises 14 symbols and 1200sub-carriers spread across a 20 MHz bandwidth. The smallest allocationof user data for transmission in LTE is a resource block comprisingtwelve sub-carriers transmitted over one slot (0.5 subframe). Forclarity, in FIG. 3, each individual resource element is not shown,instead each individual box in the subframe grid corresponds to twelvesub-carriers transmitted on one symbol.

FIG. 3 shows in hatching resource allocations for four LTE terminals340, 341, 342, 343. For example, the resource allocation 342 for a firstLTE terminal (UE 1) extends over five blocks of twelve sub-carriers(i.e. 60 sub-carriers), the resource allocation 343 for a second LTEterminal (UE2) extends over six blocks of twelve sub-carriers and so on.

Control channel data is transmitted in a control region 300 (indicatedby dotted-shading in FIG. 3) of the subframe comprising the first nsymbols of the subframe where n can vary between one and three symbolsfor channel bandwidths of 3 MHz or greater and where n can vary betweentwo and four symbols for channel bandwidths of 1.4 MHz. For the sake ofproviding a concrete example, the following description relates to hostcarriers with a channel bandwidth of 3 MHz or greater so the maximumvalue of n will be 3. The data transmitted in the control region 300includes data transmitted on the physical downlink control channel(PDCCH), the physical control format indicator channel (PCFICH) and thephysical HARQ indicator channel (PHICH).

PDCCH contains control data indicating which sub-carriers on whichsymbols of the subframe have been allocated to specific LTE terminals.Thus, the PDCCH data transmitted in the control region 300 of thesubframe shown in FIG. 3 would indicate that UE1 has been allocated theblock of resources identified by reference numeral 342, that UE2 hasbeen allocated the block of resources identified by reference numeral343, and so on.

PCFICH contains control data indicating the size of the control region(i.e. between one and three symbols).

PHICH contains HARQ (Hybrid Automatic Request) data indicating whetheror not previously transmitted uplink data has been successfully receivedby the network.

Symbols in a central band 310 of the time-frequency resource grid areused for the transmission of information including the primarysynchronisation signal (PSS), the secondary synchronisation signal (SSS)and the physical broadcast channel (PBCH). This central band 310 istypically 72 sub-carriers wide (corresponding to a transmissionbandwidth of 1.08 MHz). The PSS and SSS are synchronisation signals thatonce detected allow an LTE terminal device to achieve framesynchronisation and determine the cell identity of the enhanced Node Btransmitting the downlink signal. The PBCH carries information about thecell, comprising a master information block (MIB) that includesparameters that LTE terminals use to properly access the cell. Datatransmitted to individual LTE terminals on the physical downlink sharedchannel (PDSCH) can be transmitted in other resource elements of thesubframe. Further explanation of these channels is provided below.

FIG. 3 also shows a region of PDSCH containing system information andextending over a bandwidth of R₃₄₄. A conventional LTE frame will alsoinclude reference signals which are discussed further below but notshown in FIG. 3 in the interests of clarity.

The number of sub-carriers in an LTE channel can vary depending on theconfiguration of the transmission network. Typically this variation isfrom 72 sub carriers contained within a 1.4 MHz channel bandwidth to1200 sub-carriers contained within a 20 MHz channel bandwidth (asschematically shown in FIG. 3). As is known in the art, data transmittedon the PDCCH, PCFICH and PHICH is typically distributed on thesub-carriers across the entire bandwidth of the subframe to provide forfrequency diversity. Therefore a conventional LTE terminal must be ableto receive the entire channel bandwidth in order to receive and decodethe control region.

FIG. 4 illustrates an LTE “camp-on” process, that is, the processfollowed by a terminal so that it can decode downlink transmissionswhich are sent by a base station via a downlink channel. Using thisprocess, the terminal can identify the parts of the transmissions thatinclude system information for the cell and thus decode configurationinformation for the cell.

As can be seen in FIG. 4, in a conventional LTE camp-on procedure, theterminal first synchronizes with the base station (step 400) using thePSS and SSS in the centre band and then decodes the PBCH (step 401).Once the terminal has performed steps 400 and 401, it is synchronizedwith the base station.

For each subframe, the terminal then decodes the PCFICH which isdistributed across the entire bandwidth of carrier 320 (step 402). Asdiscussed above, an LTE downlink carrier can be up to 20 MHz wide (1200sub-carriers) and an LTE terminal therefore has to have the capabilityto receive and decode transmissions on a 20 MHz bandwidth in order todecode the PCFICH. At the PCFICH decoding stage, with a 20 MHz carrierband, the terminal operates at a much larger bandwidth (bandwidth ofR₃₂₀) than during steps 400 and 401 (bandwidth of R₃₁₀) relating tosynchronization and PBCH decoding.

The terminal then ascertains the PHICH locations (step 403) and decodesthe PDCCH (step 404), in particular for identifying system informationtransmissions and for identifying its resource allocations. The resourceallocations are used by the terminal to locate system information and tolocate its data in the PDSCH as well as to be informed of anytransmission resources it has been granted on PUSCH. Both systeminformation and UE-specific resource allocations are transmitted onPDSCH and scheduled within the carrier band 320. Steps 403 and 404 alsorequire the terminal to operate on the entire bandwidth R320 of thecarrier band.

At steps 402 to 404, the terminal decodes information contained in thecontrol region 300 of a subframe. As explained above, in LTE, the threecontrol channels mentioned above (PCFICH, PHICH and PDCCH) can be foundacross the control region 300 of the carrier where the control regionextends over the range R₃₂₀ and occupies the first one, two or threeOFDM symbols of each subframe as discussed above. In a subframe,typically the control channels do not use all the resource elementswithin the control region 300, but they are scattered across the entireregion, such that a LTE terminal has to be able to simultaneouslyreceive the entire control region 300 for decoding each of the threecontrol channels.

The terminal can then decode the PDSCH (step 405) which contains systeminformation or data transmitted for this terminal.

As explained above, in an LTE subframe the PDSCH generally occupiesgroups of resource elements which are neither in the control region norin the resource elements occupied by PSS, SSS or PBCH. The data in theblocks of resource elements 340, 341, 342, 343 allocated to thedifferent mobile communication terminals (UEs) shown in FIG. 3 have asmaller bandwidth than the bandwidth of the entire carrier, although todecode these blocks a terminal first receives the PDCCH spread acrossthe frequency range R₃₂₀ to determine if the PDCCH indicates that aPDSCH resource is allocated to the UE and should be decoded. Once a UEhas received the entire subframe, it can then decode the PDSCH in therelevant frequency range (if any) indicated by the PDCCH. So forexample, UE 1 discussed above decodes the whole control region 300 andthen the data in the resource block 342.

Virtual Downlink Carrier

Certain classes of devices, such as MTC devices (e.g. semi-autonomous orautonomous wireless communication devices such as smart meters asdiscussed above), support communication applications that arecharacterised by the transmission of small amounts of data at relativelyinfrequent intervals and can thus be considerably less complex thanconventional LTE terminals. In many scenarios, providing low capabilityterminals such as those with a conventional high-performance LTEreceiver unit capable of receiving and processing data from an LTEdownlink frame across the full carrier bandwidth can be overly complexfor a device which only needs to communicate small amounts of data. Thismay therefore limit the practicality of a widespread deployment of lowcapability MTC type devices in an LTE network. It is preferable insteadto provide low capability terminals such as MTC devices with a simplerreceiver unit which is more proportionate with the amount of data likelyto be transmitted to the terminal. As set out below, in accordance withexamples of the present invention a “virtual carrier” is provided withinthe transmission resources of a conventional OFDM type downlink carrier(i.e. a “host carrier”). Unlike data transmitted on a conventional OFDMtype downlink carrier, data transmitted on the virtual carrier can bereceived and decoded without needing to process the full bandwidth ofthe downlink host OFDM carrier. Accordingly, data transmitted on thevirtual carrier can be received and decoded using a reduced complexityreceiver unit.

FIG. 5 provides a schematic diagram illustrating an LTE downlinksubframe which includes a virtual carrier inserted in a host carrier inaccordance with an example of the present invention.

In keeping with a conventional LTE downlink subframe, the first nsymbols (n is three in FIG. 5) form the control region 300 which isreserved for the transmission of downlink control data such as datatransmitted on the PDCCH. However, as can be seen from FIG. 5, outsideof the control region 300 the LTE downlink subframe includes a group ofresource elements positioned in this example below the central band 310which form a virtual carrier 501. As explained further below, thevirtual carrier 501 is adapted so that data transmitted on the virtualcarrier 501 can be treated as logically distinct from data transmittedin the remaining parts of the host carrier and can be decoded withoutdecoding all the control data from the control region 300. Although FIG.5 shows the virtual carrier occupying frequency resources below thecentre band, in general the virtual carrier can occupy other frequencyresources, for example, above the centre band or including the centreband. If the virtual carrier is configured to overlap any resources usedby the PSS, SSS or PBCH of the host carrier, or any other signaltransmitted by the host carrier that a terminal device operating on thehost carrier would require for correct operation and expect to find in aknown pre-determined location, the signals on the virtual carrier can bearranged such that these aspects of the host carrier signal aremaintained.

As can be seen from FIG. 5, data transmitted on the virtual carrier 501is transmitted across a limited bandwidth. This might be any suitablebandwidth smaller than that of the host carrier. In the example shown inFIG. 5 the virtual carrier is transmitted across a bandwidth comprising12 blocks of 12 sub-carriers (i.e. 144 sub-carriers), which isequivalent to a 2.16 MHz transmission bandwidth. Accordingly, a terminalusing the virtual carrier need only be equipped with a receiver capableof receiving and processing data transmitted over a bandwidth of 2.16MHz. This enables low capability terminals (for example MTC typeterminals) to be provided with simplified receiver units yet still beable to operate within an OFDM type communication network which, asexplained above, conventionally requires terminals to be equipped withreceivers capable of receiving and processing an OFDM signal across theentire bandwidth of the signal.

As explained above, in OFDM-based mobile communication systems such asLTE, downlink data is dynamically assigned to be transmitted ondifferent sub-carriers on a subframe by subframe basis. Accordingly, inevery subframe the network signals which sub-carriers on which symbolscontain data relevant to which terminals (i.e. downlink allocationsignalling).

As can be seen from FIG. 3, in a conventional downlink LTE subframe thisinformation is transmitted on the PDCCH during the first symbol orsymbols of the subframe. However, as previously explained, theinformation transmitted in the PDCCH is spread across the entirebandwidth of the subframe and therefore cannot be received by a mobilecommunication terminal with a simplified receiver unit capable only ofreceiving the reduced bandwidth virtual carrier.

Accordingly, as can be seen in FIG. 5, the final symbols of the virtualcarrier can be reserved as a control region 502 for the virtual carrierfor the transmission of control data indicating which resource elementsof the virtual carrier 501 have been allocated to user equipment (UEs)using the virtual carrier. In some examples the number of symbolscomprising the virtual carrier control region 502 might be fixed, forexample three symbols. In other examples the virtual carrier controlregion 502 can vary in size, for example between one and three symbols,as with the control region 300.

The virtual carrier control region can be located at any suitableposition, for example in the first few symbols of the virtual carrier.In the example of FIG. 5 this could mean positioning the virtual carriercontrol region on the fourth, fifth and sixth symbols. However, fixingthe position of the virtual carrier control region in the final symbolsof the subframe can be useful because the position of the virtualcarrier control region will not vary in dependence on the number ofsymbols of the host carrier control region 300. This can help simplifythe processing undertaken by mobile communication terminals receivingdata on the virtual carrier because there is no need for terminals todetermine a position of the virtual carrier control region everysubframe if it is known that it will always be positioned in the final nsymbols of the subframe.

In a further embodiment, the virtual carrier control symbols mayreference virtual carrier PDSCH transmissions in a separate subframe.

In some examples the virtual carrier may be located within the centreband 310 of the downlink subframe. This can help reduce the impact onhost carrier PDSCH resources caused by the introduction of the virtualcarrier within the host carrier bandwidth since the resources occupiedby the PSS/SSS and PBCH would be contained within the virtual carrierregion and not the remaining host carrier PDSCH region. Therefore,depending on for example the expected virtual carrier throughput, thelocation of a virtual carrier can be appropriately chosen to eitherexist inside or outside the centre band according to whether the host orvirtual carrier is chosen to bear the overhead of the PSS, SSS and PBCH.

Virtual Carrier “Camp-On” Process

As explained above, before a conventional LTE terminal can begintransmitting and receiving data in a cell, it first camps on to thecell. An adapted camp-on process can be provided for terminals using thevirtual carrier.

FIG. 6 shows a flow diagram schematically illustrating a camp-on processaccording to an example of the present invention. There are two branchesshown in FIG. 6. Different steps of the process associated with a UEintending to use the virtual carrier are shown under the general heading“virtual carrier”. The steps shown under the general heading “legacyLTE” are associated with a UE intending to use the host carrier, andthese steps correspond to the steps of FIG. 4. In this example, thefirst two steps 400, 401 of the camp-on procedure are common to both thevirtual carrier and host (legacy LTE) carrier.

The virtual carrier camp-on process is explained with reference to theexample subframe shown in FIG. 5 in which a virtual carrier with abandwidth of 144 sub-carriers is inserted within the operating bandwidthof a host carrier with a bandwidth corresponding to 1200 sub-carriers.As discussed above, a terminal having a receiver unit with anoperational bandwidth of less than that of the host carrier cannot fullydecode data in the control region of subframes of the host carrier.However, a receiver unit of a terminal having an operational bandwidthof only twelve blocks of twelve sub-carriers (i.e. 2.16 MHz) can receivecontrol and user data transmitted on this example virtual carrier 502.

As noted above, in the example of FIG. 6, the first steps 400 and 401for a virtual carrier terminal are the same as the conventional camp-onprocess shown in FIG. 4, although a virtual carrier terminal may extractadditional information from the MIB as described below. Both types ofterminals (i.e. virtual carrier terminals and host/legacy carrierterminals) can use the PSS/SSS and PBCH to synchronize with the basestation using the information carried on the 72 sub-carrier centre bandwithin the host carrier. However, where the conventional LTE terminalsthen continue with the process by performing the PCFICH decoding step402, which requires a receiver unit capable of receiving and decodingthe host carrier control region 300, a terminal camping on to the cellto receive data on the virtual carrier (which may be referred to as a“virtual carrier terminal”) performs steps 606 and 607 instead.

In a further example a separate synchronisation and PBCH functionalitycan be provided for the virtual carrier device as opposed to re-usingthe same conventional initial camp-on processes of steps 400 and 401 ofthe host carrier device.

At step 606, the virtual carrier terminal locates a virtual carrier, ifany is provided within the host carrier, using a virtualcarrier-specific step. Various examples of how this step may beperformed are discussed further below. Once the virtual carrier terminalhas located a virtual carrier, it can access information within thevirtual carrier. For example, if the virtual carrier mirrors theconventional LTE resource allocation method, the virtual carrierterminal may proceed to decode control portions within the virtualcarrier, which can, for example, indicate which resource elements withinthe virtual carrier have been allocated for a specific virtual carrierterminal or for system information. For example, FIG. 7 shows the blocksof resource elements 350 to 352 within virtual carrier 330 that havebeen allocated for the subframe SF2. However, there is no requirementfor the virtual carrier terminal to follow or mirror the conventionalLTE process (e.g. steps 402-404) and these steps may for example beimplemented very differently for a virtual carrier camp-on process.

Regardless of the virtual carrier terminal following a LTE-like step ora different type of step when performing step 607, the virtual carrierterminal can then decode the allocated resource elements at step 608 andthereby receive data transmitted by the base station broadcasting thevirtual carrier. The data decoded in step 608 may include, for example,the remainder of the system information containing details of thenetwork configuration.

Even though the virtual carrier terminal does not have the bandwidthcapabilities to decode and receive downlink data if it was transmittedin the host carrier using conventional LTE, it can still access avirtual carrier within the host carrier having a limited bandwidthwhilst re-using the initial LTE steps. Step 608 may also be implementedin a LTE-like manner or in a different manner. For example, multiplevirtual carrier terminals may share a virtual carrier and have grantsallocated to manage the virtual carrier sharing as shown in SF2 in FIG.7, or, in another example, a virtual carrier terminal may have theentire virtual carrier allocated for its own downlink transmissions, orthe virtual carrier may be entirely allocated to a virtual carrierterminal for a certain number of subframe only, etc.

There is thus a large degree of flexibility provided for the virtualcarrier camp-on process. There is, for example, the ability to adjust abalance between re-using or mirroring conventional LTE steps orprocesses, thereby reducing the terminal complexity and the need toimplement new elements, and adding new virtual carrier specific aspectsor implementations, thereby potentially optimizing the use ofnarrow-band virtual carriers, as LTE has been designed with thelarger-band host carriers in mind.

Downlink Virtual Carrier Detection

As discussed above, the virtual carrier terminal should locate (withinthe time-frequency resource grid of the host carrier) the virtualcarrier before it can receive and decode transmissions on the virtualcarrier. Several alternatives are available for the virtual carrierpresence and location determination, which can be implemented separatelyor in combination. Some of these options are discussed below.

To facilitate the virtual carrier detection, the virtual carrierlocation information may be provided to the virtual carrier terminalsuch that it can locate the virtual carrier, if any exists, more easily.For example, such location information may comprise an indication thatone or more virtual carriers are provided within the host carrier, orthat the host carrier does not currently provide any virtual carrier. Itmay also comprise an indication of the virtual carrier's bandwidth, forexample in MHz or blocks of resource elements. Alternatively, or incombination, the virtual carrier location information may comprise thevirtual carrier's centre frequency and bandwidth, thereby giving thevirtual carrier terminal the location and bandwidth of any activevirtual carrier. In the event the virtual carrier is to be found at adifferent frequency position in each subframe, according, for example,to a pseudo-random hopping algorithm, the location information can, forexample, indicate a pseudo random parameter. Such parameters may includea starting frame and parameters used for the pseudo-random algorithm.Using these pseudo-random parameters, the virtual carrier terminal canthen know where the virtual carrier can be found for any subframe.

On implementation feature associated with little change to the virtualcarrier terminal (as compared with a conventional LTE terminal) would beto include location information for the virtual carrier within the PBCH,which already carries the Master Information Block, or MIB in the hostcarrier centre band. As shown in FIG. 8, the MIB consists of 24 bits (3bits to indicate DL bandwidth, 8 bits to indicate the System FrameNumber or SFN, and 3 bits regarding the PHICH configuration). The MIBtherefore comprises 10 spare bits that can be used to carry locationinformation in respect of one or more virtual carriers. For example,FIG. 9 shows an example where the PBCH includes the MIB and locationinformation (“LI”) for pointing any virtual carrier terminal to avirtual carrier.

Alternatively, virtual carrier location information could be provided inthe centre band, outside of the PBCH. It can for example be alwaysprovided after and adjacent to the PBCH. By providing the locationinformation in the centre band but outside of the PBCH, the conventionalPBCH is not modified for the purpose of using virtual carriers, but avirtual carrier terminal can easily find the location information inorder to detect the virtual carrier, if any.

The virtual carrier location information, if provided, can be providedelsewhere in the host carrier, but it may be advantageous to provide itin the centre band, for example because a virtual carrier terminal mayconfigure its receiver to operate on the centre band and the virtualcarrier terminal then does not need to adjust its receiver settings forfinding the location information.

Depending on the amount of virtual carrier location informationprovided, the virtual carrier terminal can either adjust its receiver toreceive the virtual carrier transmissions, or it may require furtherlocation information before it can do so.

If for example, the virtual carrier terminal was provided with locationinformation indicating a virtual carrier presence and/or a virtualcarrier bandwidth but not indicating any details as to the exact virtualcarrier frequency range, or if the virtual carrier terminal was notprovided with any location information, the virtual carrier terminalcould then scan the host carrier for a virtual carrier (e.g. performinga so-called blind search process). Scanning the host carrier for avirtual carrier can be based on different approaches, some of which willbe presented below.

According to a first approach, a virtual carrier might only be insertedin certain pre-determined locations, as illustrated for example in FIG.10 for a four-location example. The virtual carrier terminal then scansthe four locations L1-L4 for any virtual carrier. If and when thevirtual carrier terminal detects a virtual carrier, it can then“camp-on” the virtual carrier to receive downlink data as describedabove. In this approach, the virtual carrier terminal may be providedwith the possible virtual carrier locations in advance, for example theymay be stored as a network-specific setting in an internal memory.Detection of a virtual carrier could be accomplished by seeking todecode a particular physical channel on the virtual carrier. Thesuccessful decoding of such a channel, indicated for example by asuccessful cyclic redundancy check (CRC) on decoded data, would indicatethe successful location of the virtual carrier

According to a second approach, the virtual carrier may include locationsignals such that a virtual carrier terminal scanning the host carriercan detect such signals to identify the presence of a virtual carrier.Examples of possible location signals are illustrated in FIGS. 11A to11D. In the examples of FIGS. 11A to 11C, the virtual carrier regularlysends an arbitrary location signal such that a terminal scanning afrequency range where the location signal is would detect this signal.An “arbitrary” signal is intended here to include any signal that doesnot carry any information as such, or is not meant to be interpreted,but merely includes a specific signal or pattern that a virtual carrierterminal can detect. This can for example be a series of positive bitsacross the entire location signal, an alternation of 0 and 1 across thelocation signal, or any other suitable arbitrary signal. It isnoteworthy that the location signal may be made of adjacent blocks ofresource elements or may be formed of non-adjacent blocks. For example,it may be located at every other block of resource elements at the “top”(i.e. upper frequency limit) of the virtual carrier.

In the example of FIG. 11A, the location signal 353 extends across therange R₃₃₀ of the virtual carrier 330 and is always found at the sameposition in the virtual carrier within a subframe. If the virtualcarrier terminal knows where to look for a location signal in a virtualcarrier subframe, it can then simplify its scanning process by onlyscanning this position within a subframe for a location signal. FIG. 11Bshows a similar example where every subframe includes a location signal354 comprising two parts: one at the top corner and one at the bottomcorner of the virtual carrier subframe, at the end of this subframe.Such a location signal may be useful if, for example, the virtualcarrier terminal does not know the bandwidth of the virtual carrier inadvance as it can facilitate a clear detection of the top and bottomfrequency edges of the virtual carrier band.

In the example of FIG. 11C, a location signal 355 is provided in a firstsubframe SF1, but not in a second subframe SF2. The location signal canfor example be provided every two subframes. The frequency of thelocation signals can be chosen to adjust a balance between reducingscanning time and reducing overhead. In other words, the more often thelocation signal is provided, the less long it takes a terminal to detecta virtual carrier but the more overhead there is.

In the example of FIG. 11D, a location signal is provided where thislocation signal is not an arbitrary signal as in FIGS. 11A to 11C, butis a signal that includes information for virtual carrier terminals. Thevirtual carrier terminals can detect this signal when they scan for avirtual carrier and the signal may include information in respect of,for example, the virtual carrier bandwidth or any other virtualcarrier-related information (location or non-location information). Whendetecting this signal, the virtual carrier terminal can thereby detectthe presence and location of the virtual carrier. As shown in FIG. 11D,the location signal can, like an arbitrary location signal, be found atdifferent locations within the subframe, and the location may vary on aper-subframe basis.

Dynamic Variation of Control Region Size of Host Carrier

As explained above, in LTE the number of symbols that make up thecontrol region of a downlink subframe varies dynamically depending onthe quantity of control data that needs to be transmitted. Typically,this variation is between one and three symbols. As will be understoodwith reference to FIG. 5, variation in the width of the host carriercontrol region will cause a corresponding variance in the number ofsymbols available for the virtual carrier. For example, as can be seenin FIG. 5, when the control region is three symbols in length and thereare 14 symbols in the subframe, the virtual carrier is eleven symbolslong. However, if in the next subframe the control region of the hostcarrier were reduced to one symbol, there would be thirteen symbolsavailable for the virtual carrier in that subframe.

When a virtual carrier is inserted into a LTE host carrier, mobilecommunication terminals receiving data on the virtual carrier need to beable to determine the number of symbols in the control region of eachhost carrier subframe to determine the number of symbols in the virtualcarrier in that subframe if they are to be able to use all availablesymbols that are not used by the host carrier control region.

Conventionally, the number of symbols forming the control region issignalled in the first symbol of every subframe in the PCFICH. However,the PCFICH is typically distributed across the entire bandwidth of thedownlink LTE subframe and is therefore transmitted on sub-carriers whichvirtual carrier terminals capable only of receiving the virtual carriercannot receive. Accordingly, in one embodiment, any symbols across whichthe control region could possibly extend are predefined as null symbolson the virtual carrier, i.e. the length of the virtual sub-carrier isset at (m−n) symbols, where m is the total number of symbols in asubframe and n is the maximum number of symbols of the control region.Thus, resource elements are never allocated for downlink datatransmission on the virtual carrier during the first n symbols of anygiven subframe.

Although this embodiment is simple to implement it will be spectrallyinefficient because during subframes when the control region of the hostcarrier has fewer than the maximum number of symbols, there will beunused symbols in the virtual carrier.

In another embodiment, the number of symbols in the control region ofthe host carrier is explicitly signalled in the virtual carrier itself.Once the number of symbols in the control region of the host carrier isknown, the number of symbols in the virtual carrier can be calculated bysubtracting the total number of symbols in the subframe from thisnumber.

In one example an explicit indication of the host carrier control regionsize is given by certain information bits in the virtual carrier controlregion. In other words an explicit signalling message is inserted at apredefined position in the virtual carrier control region 502. Thispredefined position is known by each terminal adapted to receive data onthe virtual carrier.

In another example, the virtual carrier includes a predefined signal,the location of which indicates the number of symbols in the controlregion of the host carriers. For example, a predefined signal could betransmitted on one of three predetermined blocks of resource elements.When a terminal receives the subframe it scans for the predefinedsignal. If the predefined signal is found in the first block of resourceelements this indicates that the control region of the host carriercomprises one symbol; if the predefined signal is found in the secondblock of resource elements this indicates that the control region of thehost carrier comprises two symbols and if the predefined signal is foundin the third block of resource elements this indicates that the controlregion of the host carrier comprises three symbols.

In another example, the virtual carrier terminal is arranged to firstattempt to decode the virtual carrier assuming that the control regionsize of the host carrier is one symbol. If this is not successful, thevirtual carrier terminal attempts to decode the virtual carrier assumingthat the control region size of the host carrier is two and so on, untilthe virtual carrier terminal successfully decodes the virtual carrier.

Downlink Virtual Carrier Reference Signals

As is known in the art, in OFDM-based transmission systems, such as LTE,a number of sub-carriers in symbols throughout the subframes aretypically reserved for the transmission of reference signals. Asexplained further below, reference symbols play a significant role insome embodiments of the invention. However, some conventional aspects ofreference symbols are first described. Reference signals areconventionally transmitted on sub-carriers distributed throughout asubframe across the channel bandwidth and across the OFDM symbols. Thereference signals are arranged in a repeating pattern and can be used bya receiver to estimate the channel function applied to the datatransmitted on each sub-carrier using extrapolation and interpolationtechniques. These reference signals are also typically used foradditional purposes such as determining metrics for received signalpower indications, automatic frequency control metrics and automaticgain control metrics. In LTE the positions of the reference signalbearing sub-carriers within each subframe are pre-determined and knownat the transceiver of each terminal.

In a conventional LTE downlink subframes, there are a number ofdifferent reference signals, transmitted for different purposes. Oneexample is the cell-specific reference signal, broadcast to allterminals. Cell-specific reference symbols are typically inserted onevery sixth sub-carrier on each transmit antenna port on which theyoccur. Accordingly, if a virtual carrier is inserted in an LTE downlinksubframe, even if the virtual carrier has a minimum bandwidth of oneresource block (i.e. twelve sub-carriers) the virtual carrier willinclude at least some cell-specific reference signal bearingsub-carriers.

There are sufficient reference signal bearing sub-carriers provided ineach subframe such that a receiver need not accurately receive everysingle reference signal to decode the data transmitted in the subframe.However, as will be understood the more reference signals that arereceived, the better a receiver will generally be able to estimate thechannel response, and hence fewer errors will typically be introducedinto the data decoded from the subframe. Accordingly, in order topreserve compatibility with LTE communication terminals receiving dataon the host carrier, in accordance with some examples of the presentinvention, the sub-carrier positions that would contain referencesignals in a conventional LTE subframe are retained in the virtualcarrier, subject to the exceptions discussed further below in accordancewith embodiments of the invention.

As will be understood, in accordance with examples of the presentinvention, terminals arranged to receive only the virtual carrierreceive a reduced number of sub-carriers compared to conventional LTEterminals which receive each subframe across the entire bandwidth of thesubframe. As a result, the reduced capability terminals receive fewerreference signals over a narrower range of frequencies which may resultin a less accurate channel estimation being generated.

In some examples a simplified virtual carrier terminal may have a lowermobility which requires fewer reference symbols to support channelestimation. However, in some examples of the present invention thedownlink virtual carrier may include additional reference signal bearingsub-carriers to enhance the accuracy of the channel estimation that thereduced capability terminals can generate (i.e. there may be a greaterdensity of reference symbols on the virtual carrier as compared to otherregions on the host carrier).

In some examples the positions of the additional reference bearingsub-carriers are such that they are systematically interspersed withrespect to the positions of the conventional reference signal bearingsub-carriers thereby increasing the sampling frequency of the channelestimation when combined with the reference signals from the existingreference signal bearing sub-carriers. This allows an improved channelestimation of the channel to be generated by the reduced capabilityterminals across the bandwidth of the virtual carrier. In otherexamples, the positions of the additional reference bearing sub-carriersare such that they are systematically placed at the edge of thebandwidth of the virtual carrier thereby increasing the interpolationaccuracy of the virtual carrier channel estimates.

Alternative Virtual Carrier Arrangements

So far examples of the invention have been described generally in termsof a host carrier in which a single virtual carrier has been inserted asshown for example in FIG. 5. However, in some examples a host carriermay include more than one virtual carrier as shown for example in FIG.12. FIG. 12 shows an example in which two virtual carriers VC1 (330) andVC2 (331) are provided within a host carrier 320. In this example, thetwo virtual carriers change location within the host carrier bandaccording to a pseudo-random algorithm. However, in other examples, oneor both of the two virtual carriers may always be found in the samefrequency range within the host carrier frequency range and/or maychange position according to a different mechanism. In LTE, the numberof virtual carriers within a host carrier is only limited by the size ofthe host carrier. However, too many virtual carriers within the hostcarrier may unduly limit the bandwidth available for transmitting datato conventional LTE terminals and an operator may therefore decide on anumber of virtual carrier within a host carrier according to, forexample, a ratio of conventional LTE users/virtual carrier users.

In some examples the number of active virtual carriers can bedynamically adjusted such that it fits the current needs of conventionalLTE terminals and virtual carrier terminals. For example, if no virtualcarrier terminal is connected or if their access is to be intentionallylimited, the network can arrange to begin scheduling the transmission ofdata to LTE terminals within the sub-carriers previously reserved forthe virtual carrier. This process can be reversed if the number ofactive virtual carrier terminals begins to increase. In some examplesthe number of virtual carriers provided may be increased in response toan increase in the presence of virtual carrier terminals. For example ifthe number of virtual carrier terminals present in a network or area ofa network exceeds a threshold value, an additional virtual carrier isinserted in the host carrier. The network elements and/or networkoperator can thus activate or deactivate the virtual carriers wheneverappropriate.

The virtual carrier shown for example in FIG. 5 is 144 sub-carriers inbandwidth. However, in other examples a virtual carrier may be of anysize between twelve sub-carriers to 1188 sub-carriers (for a carrierwith a 1200 sub-carrier transmission bandwidth). Because in LTE thecentre band has a bandwidth of 72 sub-carriers, a virtual carrierterminal in an LTE environment preferentially has a receiver bandwidthof at least 72 sub-carriers (1.08 MHz) such that it can decode thecentre band 310, therefore a 72 sub-carrier virtual carrier may providea convenient implementation option. With a virtual carrier comprising 72sub-carriers, the virtual carrier terminal does not have to adjust thereceiver's bandwidth for camping on the virtual carrier which maytherefore reduce complexity of performing the camp-on process, but thereis no requirement to have the same bandwidth for the virtual carrier asfor the centre band and, as explained above, a virtual carrier based onLTE can be of any size between 12 to 1188 sub-carriers. For example, insome systems, a virtual carrier having a bandwidth of less than 72sub-carriers may be considered as a waste of the virtual carrierterminal's receiver resources, but from another point of view, it may beconsidered as reducing the impact of the virtual carrier on the hostcarrier by increasing the bandwidth available to conventional LTEterminals. The bandwidth of a virtual carrier can therefore be adjustedto achieve the desired balance between complexity, resource utilization,host carrier performance and requirements for virtual carrier terminals.

Uplink Transmission Frame

So far, the virtual carrier has been discussed primarily with referenceto the downlink, however in some examples a virtual carrier can also beinserted in the uplink.

In frequency division duplex (FDD) networks both the uplink and downlinkare active in all subframes, whereas in time division duplex (TDD)networks subframes can either be assigned to the uplink, to thedownlink, or further sub-divided into uplink and downlink portions.

In order to initiate a connection to a network, conventional LTEterminals make a random access request on the physical random accesschannel (PRACH). The PRACH is located in predetermined blocks ofresource elements in the uplink frame, the positions of which aresignaled to the LTE terminals in the system information signaled on thedownlink.

Additionally, when there is pending uplink data to be transmitted froman LTE terminal and the terminal does not already have any uplinkresources allocated to it, it can transmit a random access request PRACHto the base station. A decision is then made at the base station as towhich if any uplink resource is to be allocated to the terminal devicethat has made the request. Uplink resource allocations are then signaledto the LTE terminal on the physical downlink control channel (PDCCH)transmitted in the control region of the downlink subframe.

In LTE, transmissions from each terminal device are constrained tooccupy a set of contiguous resource blocks in a frame. For the physicaluplink shared channel (PUSCH) the uplink resource allocation grantreceived from the base station will indicate which set of resourceblocks to use for that transmission, where these resource blocks couldbe located anywhere within the channel bandwidth.

The first resources used by the LTE physical uplink control channel(PUCCH) are located at both the upper and lower edge of the channel,where each PUCCH transmission occupies one resource block. In the firsthalf of a subframe this resource block is located at one channel edge,and in the second half of a subframe this resource block is located atthe opposite channel edge. As more PUCCH resources are required,additional resource blocks are assigned in a sequential manner, movinginward from the channel edges. Since PUCCH signals are code divisionmultiplexed, an LTE uplink can accommodate multiple PUCCH transmissionsin the same resource block.

Virtual Uplink Carrier

In accordance with embodiments of the present invention, the virtualcarrier terminals described above can also be provided with a reducedcapability transmitter for transmitting uplink data. The virtual carrierterminals are arranged to transmit data across a reduced bandwidth. Theprovision of a reduced capability transmitter unit providescorresponding advantages to those achieved by providing a reducedcapability receiver unit with, for example, classes of devices that aremanufactured with a reduced capability for use with, for example, MTCtype applications.

In correspondence with the downlink virtual carrier, the virtual carrierterminals transmit uplink data across a reduced range of sub-carrierswithin a host carrier that has a greater bandwidth than that of thereduced bandwidth virtual carrier. This is shown in FIG. 13A. As can beseen from FIG. 13A, a group of sub-carriers in an uplink subframe form avirtual carrier 1301 within a host carrier 1302. Accordingly, thereduced bandwidth across which the virtual carrier terminals transmituplink data can be considered a virtual uplink carrier.

In order to implement the virtual uplink carrier, the base stationscheduler serving a virtual carrier ensures that all uplink resourceelements granted to virtual carrier terminals are sub-carriers that fallwithin the reduced bandwidth range of the reduced capability transmitterunits of the virtual carrier terminals. Correspondingly, the basestation scheduler serving the host carrier typically ensures that alluplink resource elements granted to host carrier terminals aresub-carriers that fall outside the set of sub-carriers occupied by thevirtual carrier terminals. However, if the schedulers for the virtualcarrier and the host carrier are implemented jointly, or have means toshare information, then the scheduler of the host carrier can assignresource elements from within the virtual carrier region to terminaldevices on the host carrier during subframes when the virtual carrierscheduler indicates that some or all of the virtual carrier resourceswill not be used by terminal devices on the virtual carrier.

If a virtual carrier uplink incorporates a physical channel that followsa similar structure and method of operation to the LTE PUCCH, whereresources for that physical channel are expected to be at the channeledges, for virtual carrier terminals these resources could be providedat the edges of the virtual carrier bandwidth and not at the edges ofthe host carrier. This is advantageous since it would ensure thatvirtual carrier uplink transmissions remain within the reduced virtualcarrier bandwidth.

Virtual Uplink Carrier Random Access

In accordance with conventional LTE techniques, it cannot be guaranteedthat the PRACH will be within the sub-carriers allocated to the virtualcarrier. In some embodiments therefore, the base station provides asecondary PRACH within the virtual uplink carrier, the location of whichcan be signaled to the virtual carrier terminals via system informationon the virtual carrier. This is shown for example in FIG. 13B in which aPRACH 1303 is located within the virtual carrier 1301. Thus, the virtualcarrier terminals send PRACH requests on the virtual carrier PRACHwithin the virtual uplink carrier. The position of the PRACH can besignaled to the virtual carrier terminals in a virtual carrier downlinksignaling channel, for example in system information on the virtualcarrier.

However, in other examples, the virtual carrier PRACH 1303 is situatedoutside of the virtual carrier as shown for example in FIG. 13C. Thisleaves more room within the virtual uplink carrier for the transmissionof data by the virtual carrier terminals. The position of the virtualcarrier PRACH is signaled to the virtual carrier terminals as before butin order to transmit a random access request, the virtual carrierterminals re-tune their transmitter units to the virtual carrier PRACHfrequency because it is outside of the virtual carrier. The transmitterunits are then re-tuned to the virtual carrier frequency when uplinkresource elements have been allocated.

In some examples where the virtual carrier terminals are capable oftransmitting on a PRACH outside of the virtual carrier, the position ofthe host carrier PRACH can be signaled to the virtual carrier terminals.The virtual carrier terminals can then simply use the conventional hostcarrier PRACH resource to send random access requests. This approach isadvantageous as fewer PRACH resources have to be allocated.

However, if the base station is receiving random access requests fromboth conventional LTE terminals and virtual carrier terminals on thesame PRACH resource, it is necessary that the base station is providedwith a mechanism for distinguishing between random access requests fromconventional LTE terminals and random access requests from virtualcarrier terminals.

Therefore, in some examples a time division allocation is implemented atthe base station whereby, for example, over a first set of subframes thePRACH allocation is available to the virtual carrier terminals and overa second set of subframes the PRACH allocation is available toconventional LTE terminals. Accordingly, the base station can determinethat random access requests received during the first set of subframesoriginate from virtual carrier terminals and random access requestsreceived during the second set of subframes originate from conventionalLTE terminals.

In other examples, no mechanism is provided to prevent both virtualcarrier terminals and conventional LTE terminals transmitting randomaccess requests at the same time. However, the random access preamblesthat are conventionally used to transmit a random access request aredivided into two groups. The first group is used exclusively by virtualcarrier terminals and the second group is used exclusively byconventional LTE terminals. Accordingly, the base station can determinewhether a random request originated from a conventional LTE terminal ora virtual carrier terminal simply by ascertaining to what group therandom access preamble belongs.

Example Architecture

FIG. 14 provides a schematic diagram showing part of atelecommunications system 1400 arranged in accordance with an example ofthe present invention. The telecommunications system 1400 in thisexample is based broadly on an LTE-type architecture in which a virtualcarrier, such as described above, is implemented. As such many aspectsof the operation of the telecommunications system 1400 are known andunderstood and are not described here in detail in the interest ofbrevity. Operational aspects of the telecommunications system 1400 whichare not specifically described herein may be implemented in accordancewith any known techniques, for example according to the currentLTE-standards with appropriate modifications to support virtual carriersas has been previously proposed.

Represented in FIG. 14 are three neighbouring communication cells 1404A,B, C supported by respective base stations 1401A, B, C coupled to a corenetwork 1408 and adapted in accordance with an embodiment of theinvention. In general a system such as that represented in FIG. 14 maycomprise a greater number of cells arranged to provide coverage to adesired geographic area. As is conventional for LTE-type networks, therespective base stations 1401A, B, C may communicate with one anotherover the so-called X2 interface which interconnects base stations in apeer-to-peer fashion.

Thus communication cell 1404A includes the base station (enhanced NodeB/eNB) 1401A connected to the core network 1408. The base station 1401Acomprises a transceiver unit 1410A for transmission and reception ofwireless signals and a controller unit 1411A configured to control thebase station 1401A. The controller unit 1411A may again comprise varioussub-units, such as a scheduling unit 1409A and other functional unitsfor providing functionality in accordance with embodiments of theinvention as explained further below. These sub units may be implementedas discrete hardware elements or as appropriately configured functionsof the controller unit. Thus, the controller unit 1411A may comprise aprocessor unit which is suitably configured/programmed to provide thedesired functionality described herein using conventionalprogramming/configuration techniques for equipment in wirelesstelecommunications systems. The transceiver unit 1410A and thecontroller unit 1411A are schematically shown in FIG. 14 as separateelements for ease of representation. However, it will be appreciatedthat the functionality of these units can be provided in variousdifferent ways following established practices in the art, for exampleusing a single suitably programmed integrated circuit coupled to anantenna. It will be appreciated the base station 1401A will in generalcomprise various other elements associated with its operatingfunctionality.

The base station 1401A communicates data to a plurality of conventionalLTE terminals 1402A and reduced capability terminals 1403A within thecoverage area of the cell 1404A. Each of the reduced capabilityterminals 1403A has a transceiver unit 1405A which includes a receiverunit capable of receiving data across a reduced bandwidth and atransmitter unit capable of transmitting data across a reduced bandwidthwhen compared with the capabilities of transceiver units 1406A includedin the conventional LTE terminals 1402A.

The base station 1401A is arranged to transmit downlink data using asubframe structure that supports a virtual carrier as described above,for example with reference to FIG. 5, and to receive uplink data using asubframe structure as described above, for example with reference toFIG. 13B or 13C. The reduced capability terminals 1403A are thus able toreceive and transmit data using the uplink and downlink virtual carriersas described above.

As has been explained above, because the reduced complexity terminals1403A receive and transmit data across a reduced bandwidth on the uplinkand downlink virtual carriers, the complexity, power consumption andcost of the transceiver unit 1405A needed to receive and decode downlinkdata and to encode and transmit uplink data is reduced compared to thetransceiver unit 1406A provided in the conventional LTE terminals.

When receiving downlink data from the core network 1408A to betransmitted to one of the terminals within the cell 1404A, the adaptedbase station 1401A is arranged to determine if the data is bound for aconventional LTE terminal 1402A or a reduced capability terminal 1403A.This can be achieved using any suitable technique. For example, databound for a reduced capability terminal 1403A may include a virtualcarrier flag indicating that the data should be transmitted on thedownlink virtual carrier. If the adapted base station 1401A detects thatdownlink data is to be transmitted to a reduced capability terminal1403A, an adapted scheduling unit 1409A included in the adapted basestation 1401A ensures that the downlink data is transmitted to thereduced capability terminal in question on the downlink virtual. Inanother example the network may be arranged so that the virtual carrieris logically independent of the base station. More particularly thevirtual carrier may be arranged to appear to the core network as adistinct cell so that it is not known to the core network that thevirtual carrier has any relationship with the host carrier. Packets aresimply routed to/from the virtual carrier just as they would be for aconventional cell.

In another example, packet inspection is performed at a suitable pointwithin the network to route traffic to or from the appropriate carrier(i.e. the host carrier or the virtual carrier).

In yet another example, data from the core network to the base stationis communicated on a specific logical connection for a specific terminaldevice. The base station is provided with information indicating whichlogical connection is associated with which terminal device. Informationis also provided at the base station indicating which terminal devicesare virtual carrier terminals and which are conventional LTE terminals.This information could be derived from the fact that a virtual carrierterminal would initially have connected using virtual carrier resources.In other examples virtual carrier terminals are arranged to indicatetheir capability to the base station during the connection procedure.Accordingly the base station can map data from the core network to aspecific terminal device based on whether the terminal device is avirtual carrier terminal or an LTE terminal.

When scheduling resources for the transmission of uplink data, theadapted base station 1401A is arranged to determine if the terminal tobe scheduled resources is a reduced capability terminal 1403A or aconventional LTE terminal 1402A. In some examples this is achieved byanalysing the random access request transmitted on the PRACH using thetechniques to distinguish between a virtual carrier random accessrequest and a conventional random access request as described above. Inany case, when it has been determined at the adapted base station 1401Athat a random access request has been made by a reduced capabilityterminal 1402A, the adapted scheduler 1409A is arranged to ensure thatany grants of uplink resource elements are within the virtual uplinkcarrier.

The various elements and functionality of the communication cells 1404Band 1404C are in essence the same as for the communication cell 1404A.Accordingly the elements of communication cells 1404B and 1404C aresimilar to, and will be understood from, the above description of thecorresponding elements of communication cell 1404A, and are notseparately described here on the interest of brevity.

In some examples, the virtual carrier inserted within the host carriercan be used to provide a logically distinct “network within a network”.In other words data being transmitted via the virtual carrier can betreated as logically and physically distinct from the data transmittedby the host carrier network. The virtual carrier can therefore be usedto implement what might be called a dedicated messaging network (DMN)which is “laid over” a conventional network and used to communicatemessaging data to DMN devices (i.e. virtual carrier terminals), forexample classes of MTC devices.

Further Example Applications of Virtual Carriers

Having set out the concepts of virtual carriers of the kind described inco-pending UK patent applications numbered GB 1101970.0 [2], GB1101981.7 [3], GB 1101966.8 [4], GB 1101983.3 [5], GB 1101853.8 [6], GB1101982.5 [7], GB 1101980.9 [8] and GB 1101972.6 [9], GB 1121767.6 [10]and GB 1121766.8 [11], some extensions of the virtual carrier concept inaccordance with embodiments of the invention are now described.

As noted above, it is expected that terminal devices, such as machinetype communication devices, which make use of virtual carriers mightoften be in locations with relatively high penetration loss as regardsradio communications with a base station. For example, an MTC-typeterminal device associated with a smart meter application may be locatedin a basement. This can mean certain devices using virtual carriers mayrequire a base station to transmit with significantly higher powerlevels than for other terminal devices coupled to the base station inorder to support reliable communications.

To address this issue in accordance with embodiments of the invention abase station may be configured to transmit on frequencies comprising avirtual carrier (VC) at a higher power than on frequencies comprising ahost carrier (i.e. on non-VC frequencies). The principles of thisapproach are schematically represented in FIG. 15. FIG. 15 schematicallyrepresents a maximum allowed transmission power as a function offrequency in a conventional wireless telecommunications system providingsupport for a virtual carrier as previously proposed (left-hand side ofthe figure) and in a wireless telecommunications system providingsupport for a virtual carrier in accordance with an embodiment of theinvention (right-hand side of the figure). In the conventional wirelesstelecommunications system providing support for a virtual carrier aspreviously proposed the non-VC (i.e. host) PDCCH region (represented inlight shading in FIG. 15) and the VC region (represented in dark shadingin FIG. 15) of the frequency spectrum have the same maximum allowedpower, resulting in a flat maximum power spectrum as represented in theleft-hand side of FIG. 15. In practice, communications with specificterminal devices on specific subcarriers will be made with less powerthan the maximum allowed, taking into account the conventional powercontrol mechanisms provided in wireless telecommunications systems.

However, in accordance with an embodiment of the invention, a basestation is configured to allow a higher maximum transmission power forfrequencies supporting a virtual carrier than for frequencies supportingthe non-VC traffic. This is schematically shown to the right hand sideof FIG. 15. Thus, the virtual carrier region (represented in darkshading in FIG. 15) of the frequency spectrum has a higher allowedtransmission power than the non-VC (i.e. host) PDCCH region (representedin light shading in FIG. 15). This approach can therefore allow for morereliable communications with terminal devices supported by the virtualcarrier and which might often be in “hard to reach” places, such asunderground. One significant aspect of the maximum power spectrumrepresented in the right-hand side of FIG. 15 as compared to the moreconventional approach represented in the left-hand side of FIG. 15 isthat the overall maximum power that may be transmitted by the basestation is the same in each case. That is to say, the areas under thecurves on the left- and right-hand sides of FIG. 15 are in this examplethe same. A base station providing for enhanced maximum transmissionpower on a virtual carrier may be referred to herein as supporting apower boosted virtual carrier. The actual transmission powers used ateach frequency may be determined in accordance with the principles ofconventional power control techniques in wireless telecommunicationssystems, but in accordance with embodiments of the invention, this issubject to different maximum allowed powers depending on whetherindividual subcarriers are inside or outside the range of frequenciessupporting the virtual carrier(s) in the wireless telecommunicationsnetwork. A base station in accordance with certain embodiments of theinvention may be configured to switch between the use of a power boostedvirtual carrier (i.e. a virtual carrier having a higher maximum powerthan its host carrier as indicated to the right of FIG. 15) and a“normal” power virtual carrier (i.e. a virtual carrier having the samemaximum allowed power as its host carrier as indicated to the left ofFIG. 15) according to current requirements. For example there may be noneed to adopt a power-boosted virtual carrier in subframes where thebase station is not communicating with any terminal devices whichrequire more power.

One issue with adopting a power boosted virtual carrier is an increasein the potential for intercell interference for the power boostedfrequencies of the virtual carrier. This is especially likely if aneighbouring cell is also transmitting with a power boosted virtualcarrier on overlapping frequencies. In order to help address this issue,the inventors have recognised that it can be helpful for a base stationto convey information regarding is its virtual carrier transmissions,for example information such as the frequencies used for the virtualcarrier and/or an indication of the maximum transmission powers thatmight be made on those frequencies, to neighbouring base stations.Neighbouring base stations may then take account of this informationwhen scheduling their own use of virtual carriers. For example, a firstbase station may be configured to determine in accordance with itsscheduling requirements that it should power boost a virtual carrier(i.e. the base station's transmission power budget should beconcentrated on the virtual carrier frequencies for a period of time)and may proceed in accordance with an embodiment of the invention informa neighbouring base station of this. The neighbouring base station maythen schedule its own transmissions to avoid power boosting its ownvirtual carrier on overlapping transmission resources (e.g. overlappingin terms of time and frequency).

FIG. 16 is a signalling ladder diagram representing coordination amongbase stations with regards to virtual carrier transmissions inaccordance with an embodiment of the invention. The ladder diagramrepresents three base stations corresponding with the base stations1401A, B, C represented in FIG. 14. Thus base station 1401A supportscommunications in a first cell, referred to here as cell A, while basestations 1401B and 1401C respectively support communications in secondand third communication cells, referred to here as cell B and cell C. Itis assumed here the signalling represented in the diagram starts from apoint at which the base station of cell B has elected to focus itsmaximum allowed transmission power into a virtual carrier transmitted ata frequency F_(B). It will be appreciated the virtual carrier will spana range of frequencies, and in this example it is assumed the bandwidthof the virtual carrier is fixed within the network and so the virtualcarrier frequency range may be characterised by its centre frequency.Thus in the example of FIG. 16 it is assumed base station 1401B haspreviously determined that it intends to transmit a virtual carrierhaving a centre frequency F_(B) with boosted power. In accordance withan embodiment of the invention, the base station 1401B is configured toprovide signalling to base stations of neighbouring cells, in thisexample cells A and C, to indicate its intended power boosted virtualcarrier transmissions at frequency F_(B). This signalling isschematically represented in FIG. 16 by the top two arrows from cell Bto cells A and C respectively. In an LTE-type network this signallingmay be provided using the X2 interface provided for inter-base stationcommunications. Further details on examples of how the signalling may beimplemented are provided below.

In the following discussion of the signalling ladder diagram FIG. 16 itis assumed the base station 1401A in cell A also wishes to adopt powerboosted transmissions on a virtual carrier, whereas base station 1401Cin cell C does not need to adopt any power boosted transmissions. Thismay be, for example, because the base station 1401A has data fortransmission to a terminal device which requires increased power,whereas base station 1401C does not have data for transmission to anyterminal devices which require power boosting for an upcoming schedulingperiod. Some example ways in which a base station may determine whetherit needs to make power boosted transmissions on a virtual carrier arediscussed further below.

Thus, returning to FIG. 16, in step 1601A, the base station 1401Aoperating in accordance with an embodiment of the invention determineswhether there are any neighbouring cells in which power boosting is inuse. In accordance with example of FIG. 16, the base station 1401A willdetermine that base station 1401B intends to power boost a virtualcarrier at frequency F_(B) based on the signalling previously receivedfrom base station 1401B indicating the virtual carrier frequency of cellB which is to be boosted for a period of time. The period of time may bebased on a fixed coordination cycle period, or may be variable andcommunicated between base stations as part of the information regardinga base station's intended upcoming use of power boosting.

In step 1602A, the base station 1401A operating in accordance with anembodiment of the invention determines its own virtual carrier frequencyto be power boosted. This is done by selecting from availablefrequencies in accordance with the range of virtual carrier frequenciesavailable in the network for the virtual carrier implementation at hand,while seeking to avoid overlapping with the virtual carrier frequencythat another cell as indicated will be boosted. Thus, in the example ofFIG. 16, the base station 1401A avoids power boosting on a virtualcarrier frequency F_(B), and instead selects another frequency, in thiscase F_(A), as the centre frequency for its own virtual carriertransmissions for a coming period.

Having elected to concentrate its maximum allowed transmission powerbudget into a virtual carrier transmitted at a frequency F_(A), the basestation 1401A is configured to provide signalling to base stations ofneighbouring cells, in this example cells B and C, to indicate itsintended power boosted virtual carrier transmissions at frequency F_(A).This signalling is schematically represented in FIG. 16 by the twoarrows from cell A to cells B and C respectively. This signallingcorresponds with the signalling sent from base station 1401B to bestations 1401A and 1401C earlier in the process when base station 1401Bindicated an intention to transmit a virtual carrier on frequency F_(B)with concentrated power. As mentioned above, in an LTE-type network thissignalling may be provided using the existing X2 interface provided forinter-base station communications. Further details on examples of howthe signalling may be implemented are provided below.

Having communicated its intention to make power boosted virtual carriertransmissions at frequency F_(A) to the other base stations 1401B and1401C, the base station 1401A proceeds to make transmissions with anincreased maximum allowable power on a virtual carrier at frequencyF_(A) as compared to its transmissions at frequencies outside that ofthe virtual carrier at frequency F_(A). In a similar manner, basestation 1401B makes transmissions with an increased maximum allowablepower on a virtual carrier at frequency F_(B) as compared to itstransmissions at frequencies outside that of the virtual carrier atfrequency F_(B), as it previously indicated it would do in the initialsignalling of the ladder diagram of FIG. 16. The base station 1401C,having elected not to use any power boosting, may proceed with anon-power boosted (“normal”) virtual carrier operating mode. In thisexample the frequency of the virtual carrier used by base station 1401Cmay be arbitrarily selected in accordance with this example embodimentbased on the frequencies available for virtual carrier operation in theimplementation at hand.

As noted above, the actual transmissions from the respective basestations may be made at powers which are controlled using the principlesof conventional transmission power feedback techniques, albeit withdifferent maximum allowed powers for frequencies falling within therespective virtual carrier transmissions of the base stations 1401A and1401B. For example, it may be that one of the base stations indicating adesire to allocate a higher maximum allowed power to its virtual carriertransmissions in fact is able to communicate reliably with its terminaldevices with relatively low power, for example because particularly goodchannel conditions happened to exist when the time to make thecommunications comes. In other examples each base station may beconfigured to always transmit at its maximum allowable transmissionpower for each frequency and to simply change coding rate according tochannel conditions. For example, where channel conditions areparticularly good, a higher coding rate may be used rather than a lowerpower. In such example implementations, what is referred to above as amaximum allowable transmission power may in fact be the actualtransmission power.

FIG. 17 schematically represents the respective transmissions from thebase station 1401A with power boosting on the virtual carrier atfrequency F_(A) (top left in the figure) and the base station 1401B (topright in the figure) with power boosting on the virtual carrier atfrequency F_(B) on the basis that transmissions are made at the maximumallowable transmission power for all frequencies. A combination ofsignals from base station 1401A and 1401B that might be seen by aterminal device in the vicinity of a boundary between the cellssupported by the respective base stations is schematically shown in thelower part of FIG. 17. Because the power boosted virtual carrierassociated with base station 1401A and the power boosted virtual carrierassociated with base station 1401B are at different frequencies, they donot significantly overlap, thereby helping to reduce the impact of apower boosted virtual carrier in one cell from interfering withcommunications using a power boosted virtual carrier in neighbouringcell.

Thus, in accordance with certain embodiments of the invention, basestations in a wireless telecommunications system in which virtualcarrier concept are adopted are configured to coordinate their use ofthe virtual carrier with one another. In particular, the respective basestations are configured to communicate information regarding theirintended upcoming virtual carrier transmissions, and more particularlystill, in accordance with certain embodiments the respective basestations are configured to inform neighbouring base stations of anintention to transmit a virtual carrier at an increased power comparedto a host carrier, and in some cases to furthermore indicate whatfrequency the virtual carrier is to be transmitted by that base station.Conversely, base stations in accordance with certain embodiments of theinvention are also configured to receive information from neighbouringbase stations regarding characteristics of the neighbouring basestation's intended use of a virtual carrier, and to determinecharacteristics of their own virtual carrier transmissions (e.g.frequency and use of power boosting) in a manner which takes account ofthis information received from neighbouring base stations.

In the example schematically represented in FIGS. 16 and 17 theneighbouring base stations coordinate through communications on the X2interface to help ensure each base station selects a different frequencyband in which to support a power boosted virtual carrier. However, itwill be appreciated there are other characteristics of the respectivebase stations' use of virtual carriers which can be selected byindividual base stations based on inter-base station coordination.

For example, FIG. 17 schematically represents one approach in whichdifferent base stations can coordinate to transmit their power boostedvirtual carriers at different frequencies to reduce intercellinterference arising from the potential higher powered transmissions ontheir respective virtual carriers. However, in accordance with anotherapproach according to certain embodiments of the invention neighbouringbase stations can coordinate to transmit power boosted virtual carriersat different times, instead of (or as well as) at different frequencies.For example, in some cases a wireless telecommunications system mightonly allow virtual carriers to exist at a single frequency (for examplearound a centre frequency of the host carrier bandwidth). In this caseit may not be possible for neighbouring base stations to adopt differentfrequencies for their respective power boosted virtual carriertransmissions. Accordingly, neighbouring base stations may insteadcoordinate to agree different times (i.e. different subframes) duringwhich they intend to adopt a power boosted virtual carrier. For example,a first base station in a first communication cell may determine that itneeds to adopt a power boosted virtual carrier for a given number ofsubframes to meet its scheduling requirements, and may then indicate theparticular times (subframes) on which its virtual carrier is to beboosted. For example, the base station may communicate to other basestations using the X2 interface that it intends to apply power boostingto its virtual carrier in a particular range of subframes, may, forexample for N subframes comprising every nth subframe starting fromsubframe X. If there is another base station neighbouring the first basestation which also wishes to apply power boosting, it may then determineto do so during the subframes in which the first base station has notindicated it intends to apply power boosting. It will be appreciated theprinciples underlying this approach are similar to those set out abovewith regards to the base station selecting different frequencies for thevirtual carriers, except the coordination among base stations is madewith a view to avoiding overlap in the time domain, instead of thefrequency domain. It will further be appreciated that in other examples,base stations may coordinate both in respect of their frequencies andtimes of transmission for their intended use of power boosted virtualcarriers with a view to reducing intercell interference arising from two(or more) neighbouring base stations applying power boosting on the sametime-frequency resource.

In cases where base stations are configured to coordinate is to avoidoverlapping power boosted virtual carrier transmissions in the timedomain, it may be that the coordination is made at a relatively finetemporal resolution, for example on a subframe by subframe basis, or itmay be made on a more coarse temporal resolution, for example withindividual base stations in effect reserving longer periods of timeduring which they intend to apply power boosting, for example reservingtime periods corresponding to seconds, tens of seconds, or even longer.

FIG. 18 is a flowchart schematically representing operating steps of abase station, for example, any one of the base stations 1401A, B, Crepresented in FIG. 14, in accordance with an embodiment of theinvention.

The processing represented in FIG. 18 begins in a first step S1. Asdiscussed above, processing in accordance with embodiments of theinvention is based on inter-base station coordination of characteristicsrelating to virtual carrier transmissions associated with respectivebase stations in a wireless telecommunications system. In principle,with appropriately fast signalling between base stations, coordinationcould be performed on a per-frame basis, or perhaps even a per-subframebasis. However, in practice it may be considered more appropriate foreach base station to establish characteristics associated with itsvirtual carrier transmissions for a longer period, and to exchangecoordination signalling in association with each such period, whichmight be referred to as a coordination period. For example, in oneexample a coordination period might comprise 40 frames. Thus, step S1 inFIG. 18 might correspond with the beginning of such a coordinationperiod for the base station at hand.

Thus, in step S2 the base station determines whether power boosting isneeded for the next period (i.e. the next upcoming coordination period),whatever might be (e.g. a subframe, a frame, or a predefined number ofsubframes/frames). This determination may be made by taking account ofwhich terminal devices the base station is serving which may requirepower boosted virtual carrier transmissions, for example because one ormore terminal devices is in a poor coverage area, and whether the basestation has data for transmission to any such terminal devices. Whetheror not the base station has (or will have) data for transmission to aparticular terminal in the upcoming coordination period may bedetermined in accordance with the base station's conventional schedulingoperations. Whether or not a particular terminal device is one whichrequires power boosted virtual carrier transmissions may be determinedin a number of ways, as discussed further below.

If in step S2 it is determined that power boosting is not needed, forexample because there is no data to be transmitted to any terminaldevices reliant on power boosted virtual carrier transmissions,processing may proceed from step S2 along the branch marked “no” to stepS3. In step S3 the base station proceeds to operate normally without anyvirtual carrier power boosting.

If, on the other hand, in step S2 it is determined that power boostingis needed, for example because the base station intends to transmit datato a terminal device which is in a poor coverage area in the comingperiod, processing follows the “yes” branch from step S2 to S4.

In step S4 the base station determines whether it has sufficient freeresource availability to introduce power boosting on a virtual carrierin the upcoming coordination period. For example, if the base station isalso required to support communications with a number of other terminaldevices in the upcoming coordination period, for example conventionalterminal devices served on a host carrier transmitted in parallel withthe virtual carrier, it may be that the base station cannot afford toreduce the power of transmissions on the host carrier to allow boostedtransmissions on the virtual carrier. For example, it may be that thebase station needs to maintain normal transmission powers on the hostcarrier to support the devices served by the host carrier.

If in step S4 it is determined that the base station does not havesufficient resource availability to allow it to concentratetransmissions on the virtual carrier because of the impact on the hostcarrier, processing may proceed from step S4 along the branch marked“no” to step S5. In step S5 the base station proceeds to operatenormally without any virtual carrier power boosting for the upcomingcoordination period to ensure devices other than the terminal device(s)requiring power boosted transmissions can be properly supported. Theterminal device require power boosting will thus not receive anyschedule transmissions in the upcoming coordination period. In effect,the base station is configured to wait to communicate with the terminaldevice requiring power boosting until such time as the base station cansupport power boosting on the virtual carrier without undue impact onother terminal devices being served. In this case the base station maybe configured to in effect operate normally (i.e. without virtualcarrier power boosting) for the current coordination period and toreturn to step S1 so that the steps S1 to S4 can be repeated for thenext coordination period. This approach may lead to delays incommunications with terminal devices requiring power-boostedtransmissions. However, in many cases it is expected that devicesoperating on a virtual carrier may be relatively delay tolerant suchthat the delays caused by step S5 do not represent a significant problemin practice. In some cases the base station may be configured tocontinue iterating through steps S1 to S5 to cause repeated waitingperiods in respect of particular transmissions for a particular terminaldevice until a threshold number waiting periods (iterations throughsteps S1 to S5) is reached, and then the base station may be configuredto proceed to allocate power boosted resources for communications withthe terminal device even at the cost of reduced performance for otherterminal devices. That is to say, the base station may be configuredafter a given number of iterations through steps S1 to S5 without makingtransmissions that are needed for a particular terminal device to avoidfollowing the “no” branch from step S4 to S5, even if the base stationconcludes that adopting power-boosted transmissions for the particularterminal device will impact the service provided to other terminaldevices. This approach may be appropriate to avoid a terminal devicerequiring power boosted transmissions from not receiving anytransmissions for what is considered to be too long a period (what isconsidered too long a period which will depend on the implementation athand and the extent to which the transmissions are delay tolerant).

If in step S4 it is determined that the base station has sufficientresource headroom available to allow it to concentrate its power budgetinto power boosted transmissions on a virtual carrier without causingwhat is considered too much detrimental impact on other terminal devicesin the network, processing follows the “yes” branch to step S6. Thedecision on what is considered to be an acceptable detrimental impact onother terminals in the network will depend on the implementation athand, and the devices that are being served. For example, by takingaccount of quality of service requirements associated with therespective terminal devices. As noted above, in accordance with someembodiments, processing may proceed from step S4 to step S6 even if itis determined in step S4 that virtual carrier power boosting in theupcoming period will cause a significant detrimental impact on otherterminal devices, for example because a terminal device which requirespower boosting has already been waiting for too long to receive data(i.e. there have already been too many iterations through S1 to S5 inassociation with pending transmissions for a particular terminaldevice).

In step S6 the base station is configured to determine whether it hasreceived information from any other base stations indicating theirintention to apply virtual carrier power boosting during the upcomingcoordination period. That is to say, the base station is configured todetermine whether it has received any communications such as thoseschematically represented by the top two signalling arrows in FIG. 16and discussed above.

If in step S6 it is determined that no virtual carrier power boostinformation has been received from any other base stations inassociation with the upcoming coordination period, processing followsthe branch marked “no” to step S8, discussed further below.

If, on the other hand, it is determined in step S6 that virtual carrierpower boost information has been received from another base station,processing follows the branch marked “yes” to step S7.

As discussed above, virtual carrier power boost information receivedfrom a neighbouring base station may comprise an indication ofcharacteristics associated with the neighbouring base station's upcomingintended virtual carrier transmissions. More specifically, in accordancewith certain embodiments the power boost information may comprise anindication of which transmission resources (in terms of frequenciesand/or times) the neighbouring base station intends to use for its powerboosted virtual carrier transmissions. The base station implementing theprocessing of FIG. 18 is configured to avoid using the transmissionresources that the neighbouring base station has indicated will be usedby the neighbouring base station for power boosted virtual carriertransmissions. For example, if the neighbouring base station hasindicated it intends to apply virtual carrier power boosting asdiscussed above to transmissions on resources corresponding to aparticular frequency range throughout the upcoming coordination period,the base station implementing the method of FIG. 18 is configured to ineffect consider those transmission resources as having been reserved bythe neighbouring base station for virtual carrier transmissions.

In step S8 the base station proceeds to determine which transmissionresources it intends to use for the transmissions that were establishedas being needed for the upcoming coordination period in step S2. As haspreviously been proposed for virtual carriers in wirelesstelecommunications systems, a wireless telecommunications system mightbe configured to support virtual carrier transmissions on a predefinednumber of fixed frequencies. For example, in accordance with one examplevirtual carrier implementation in a given wireless telecommunicationssystem, it may be established that base stations may only adopt virtualcarrier transmissions within four predefined frequency bands such asrepresented in FIG. 10 discussed above. In such a system, the processingin step S8 corresponds with selecting one of the allowed virtual carrierfrequency bands to adopt for power boosted transmissions. However, inother examples, a wireless telecommunications system may be configuredin such a way as to allow individual base stations to arbitrarily selectthe frequencies they are to use for virtual carrier transmissions fromanywhere within the overall system bandwidth. In this case, theprocessing in step S8 corresponds with the base station selecting afrequency band from anywhere within the system bandwidth.

However, regardless of the range of transmission resources that are madeavailable in the wireless telecommunications systems for potentialvirtual carrier transmissions by the respective base stations, inaccordance with embodiments of the invention the base station selectstransmission resources for its own upcoming power boosted transmissionsin step S8 in a manner which avoids overlap with transmission resourcesdeemed to have been already reserved by other base stations in step S7based on previously-received power boost information identified in stepS6. For example, as discussed above with reference to FIG. 16, if thewireless telecommunications system supports virtual carrier operationcentred on two frequencies, F_(A) and F_(B), and a neighbouring basestation has previously indicated it intends to use the virtual carriercomprising frequencies centred on F_(B) for power boosted transmissions,the base station implementing the processing of FIG. 18 may beconfigured in step S8 to avoid selecting these frequencies, and toinstead selects the virtual carrier frequencies centred on F_(A) for itsown power boosted virtual carrier transmissions for the upcomingcoordination period.

Having selected in step S8 the transmission resources to be used for thevirtual carrier power boosted operation in the upcoming period, the basestation is configured to generate an indication of these transmissionresources (in step S9) and to communicate this indication to other basestations (in step S10). For example, the other base stations maycomprise base stations which are geographically adjacent, or near to,the base station, such that there is a possibility of intercellinterference associated with transmissions from the respective basestations. Such other base stations might be referred to generally asneighbouring base stations.

Having selected transmission resources to be used for virtual carrierpower boosted operation (step S8), and having generated and communicatedan indication of these transmission resources to at least one other basestation (steps S9 and S10), the processing represented in FIG. 18proceeds to completion in step S11.

Thus, having reached step S11, the base station has identified thatpower boosting is needed for an upcoming period (step S2), determinedthat resources are available within the cell served by the base stationto support power boosted virtual carrier operation (step S4), selectedtransmission resources to use for the power boosted virtual carrieroperation in a manner which avoids overlap with transmission resourceswhich neighbouring base stations have indicated they intend to use forpower boosted virtual carrier operation (step S8), and communicated anindication of the transmission resources to at least one other basestation (step S10).

Having done this, the base station may proceed to schedule transmissionsfor the relevant period accordingly. For example, the base station mayoperate in a generally conventional manner apart from adopting a maximumallowed transmission power profile such as schematically represented tothe right hand side of FIG. 15, with the virtual carrier location beingbased on the selected transmission resources.

Thus, in accordance with embodiments of the invention a base station isable to coordinate with neighbouring base stations to selecttransmission resources for power boosted virtual carrier transmissionsin a manner which can help to avoid intercell interference which mightarise if neighbouring base stations both apply virtual carrier powerboosting in accordance with embodiments of the invention on overlappingtransmission resources.

The above-described example has primarily focused on using inter-basestation signalling/coordination to avoid simultaneous virtual carrieroperation by neighbouring base stations on the same frequencies throughdifferent base stations selecting different frequencies for theirvirtual carrier transmissions. However, it will of course be appreciatedthat embodiments of the invention may equally (or additionally) operateby using inter-base station signalling/coordination to avoidsimultaneous virtual carrier operation by neighbouring base stations onthe same frequencies through different base stations selecting differenttimings for their virtual carrier transmissions which might be on thesame frequency.

For example, in one implementation a wireless telecommunications systemmight allow for only a single virtual carrier frequency band, forexample at the centre of a host/system bandwidth. In this case it wouldnot generally be possible for different base stations to selectdifferent frequencies to avoid overlapping power boosted virtual carriertransmissions. Accordingly, the base stations may instead coordinate toexchange information relating to particular times in which they intendto apply power boosting to the virtual carrier transmissions. Forexample, with reference to the processing represented in FIG. 18, theinformation relating to intended virtual carrier power boost operationreceived from other base stations in step S6 and communicated to otherbase stations in step S10 might comprise an indication of which timesthe respective base stations are intending to adopt power boosting. Forexample, if in a step corresponding to step S6 of FIG. 18 a base stationreceives an indication that a neighbouring base station intends to adoptpower boosted virtual carrier operation in a particular series ofupcoming subframes, the base station may determine in a stepcorresponding to step S8 to select different subframes for its ownvirtual-carrier power boosted operation to avoid an overlap intransmission resources. Thus, the power boosted virtual carrierindication sent to neighbouring cells in a step corresponding to stepS10 of FIG. 18 may comprise an indication of which subframes areintended for power boosted virtual carrier operation by the basestation, thereby allowing other base stations to take account of thiswhen selecting their own transmission resources should they requirepower boosted virtual carrier operation in the relevant timeframe.

More generally, it will thus be appreciated that references to selectingtransmission resources should be interpreted as selecting from availabletime and/or frequencies on which virtual carrier transmissions might bemade in accordance with the specific virtual carrier implementation forthe wireless telecommunications system.

In some embodiments both time and frequency may be used to characteriseintended virtual carrier transmissions by other base stations. Forexample, a base station may receive an indication from a neighbouringbase station that the neighbouring base station intends to apply powerboosting to virtual carrier transmissions on a particular frequency andat particular times. The base station receiving such an indication andwishing to select its own transmission resources for power boostedvirtual carrier transmissions may select from non-reserved times andfrequencies to avoid overlap. In this regard, in some cases it may bepreferable seek to avoid overlapping transmission resources bypreferably selecting different times, rather than different frequencies.This approach can help a base station reduce the number of times itchanges its virtual carrier frequency as compared to what mightotherwise be required if overlap were primarily avoided throughselection of a different frequency. In some cases this can beadvantageous because switching virtual carrier frequency may lead toincreased signalling overhead and the introduction of delays while thenew virtual carrier frequency is adopted within the communication cellsupported by the base station.

As noted above, there are various ways in which a base station mightimplement step S2 in FIG. 18 to determine that there are terminaldevices requiring power boosted operation in an upcoming period. Whetheror not an individual terminal device requires scheduling in an upcomingperiod may be determined in accordance with the conventional basestation scheduling operations. However, a supplementary issue to beconsidered in step S2 in accordance with some embodiments of theinvention is whether any of the terminal devices which are to bescheduled are terminal devices which require power boostedtransmissions.

In some examples the status of particular terminal devices as beingdevices requiring power boosting may be pre-configured in the wirelesstelecommunications system. For example, the base station may simply beprovided with identities of terminal devices which might require powerboosting. Thus, the base station may be simply provided with a lookuptable of all devices within its coverage area which are defined as beingdevices requiring power boosting on the virtual carrier for reliablecommunications. This approach may be appropriate where there is lowmobility among devices. Low mobility is expected to be a typicalcharacteristic of certain classes of machine type communication devices.Thus, when a new terminal devices installed in a particular locationhaving a high propagation loss, for example a basement, a correspondingentry may be made in a lookup table at the base station supporting thelocation of the terminal device. When the base station comes to scheduletransmissions to devices in accordance with its normal schedulingoperation, it may be configured to refer to the lookup table todetermine whether any of the terminal devices to be scheduled fortransmissions are classified as devices for which power boosted virtualcarrier transmissions should be adopted.

In other examples there may be a mechanism for configuring individualterminal devices according to their status as a device requiring powerboosted transmissions. For example, software flag(s) or other settings,such as dip switches/jumpers, may be configured for a particularterminal device to be identified as one requiring power boosted virtualcarrier transmissions. A connection procedure for terminal devices inthe wireless telecommunications network may thus be modified to includea step of communicating an indication that the terminal device requirespower boosted virtual carrier operation based on this configurationsetting at the terminal device. For example, a terminal device mayestablish that it is associated with a particular terminal devicecapability/category based on such configuration settings, andcommunicate this to the base station through radio resource control(RRC) signalling or communicate the information to the core network ofthe wireless telecommunications system using NAS (Non-Access Stratumi.e. core network) signalling.

This approach is schematically represented in the signalling ladderdiagram of FIG. 19. FIG. 19 represents signalling in accordance with anembodiment of the invention between an MTC type terminal device 1403A, abase station 1401A, and a core network 1408, for example of the kindrepresented in FIG. 14. Working from the top down, in a first stepconfiguration settings are made for the terminal device 1403A toidentify it as a terminal device requiring power boosted transmissionsto support reliable communications. This configuration may be set, asdiscussed above, in software, or in hardware, for example duringinstallation of the terminal device in its particular location.

In a second step the terminal device powers on (or otherwise detects anetwork situation has changed from the previous communication) so as toinitiate an RRC setup/registration (attach) procedure in accordance withgenerally conventional techniques. In accordance with this exampleembodiment, the terminal device is configured to communicate at thisstage an indication of its status as a device requiring power boostedtransmissions. The base station 1401A receives the RRC signalling andmakes a record of the terminal device capability/category defining it asa terminal device requiring power boosted transmissions. The basestation 1401A may proceed to send signalling to the core network 1408 ifit is desired to register status information regarding the terminaldevices requirements for power boosted virtual carrier operation thecore network, and if so, the core network 1408 may provide an indication(“complete” message) to the base station 1401A to indicate this has beendone. In accordance with this example, the base station further sendsconfirmation signalling to the terminal device 1403A to confirm thestatus of the terminal device as a device requiring power boostedoperation has been recorded in the network.

This type of pre-configuration approach provides a relativelystraightforward mechanism for identifying which terminal devices requirepower boosted transmissions in a given communication cell. However, insome other examples terminal devices may be identified as terminaldevices requiring power boosted transmissions using other techniquesthat do not rely on an initial configuration. These types of approachmay be more appropriate, for example, for a terminal device which maymove from an environment in which power boosted transmissions arerequired to an environment in which power boosted transmissions are notrequired. In such circumstances it may be helpful for a terminal deviceto be able to identify its changing status in this regard throughsignalling.

Thus, a terminal device may be operable to establish whether it is in asituation which requires power-boosted transmissions in accordance withembodiments of the invention in order to support reliablecommunications. In general, this may be based on a terminal devicemaking a measurement on the extent to which it is able to receive basestation transmissions, and to report back to the base station if themeasurement indicates power boosting would be advantageous (because itwould otherwise be difficult for the terminal device to reliably receivebase station transmissions). In accordance with this approach, aterminal device may make measurements of the coverage it is receivingbased around existing mechanisms, such as those established in LTE-typewireless telecommunications systems for channel quality indicator (CQI)and pathloss reporting.

An approach based around existing CQI schemes is schematicallyrepresented in the signalling ladder diagram of FIG. 20. FIG. 20represents signalling in accordance with an embodiment of the inventionbetween an MTC type terminal device 1403A and a base station 1401A, forexample of the kind represented in FIG. 14. Working from the top down,in a first step the base station 1401A determines a reference signal tobe transmitted. In a second step the base station 1401A transmits thereference signal, and it is received by the terminal device 1403A. Fromthe received reference signal the terminal device 1403A establishes achannel quality measurement. This may be performed in accordance withgenerally conventional CQI measurement techniques for the referencesignal received. In a next step, the terminal device 1403A transmits achannel quality indicator (CQI) report to the base station 1401A. Thismay again be performed in accordance with generally conventional CQIreporting techniques in LTE-type wireless telecommunications systems.Having received the CQI report, the base station may determine from thequality of the channel received by the terminal device whether or notthe terminal device is in a location which requires power boosting dueto poor channel quality conditions.

Conventional CQI reporting in LTE-type wireless telecommunicationssystems employs so-called cell specific reference signals (CRS).However, in some cases reception of CRS may not be reliable in poorcoverage areas. Thus, a terminal device in a situation which wouldbenefit from power boosting in accordance with an embodiment of theinvention may not be able to reliably receive CRS. Thus, in accordancewith some embodiments, alternative reference signals or other equivalentsignals may be employed for CQI-type reporting. For example, theexisting DM-RS (demodulation reference signal) or CSI-RS (channel stateinformation reference signal) may be employed in LTE-based systems. Thepower settings for these reference signals can be set differently fordifferent terminal devices, thereby allowing the base station totransmit these reference signals with more power than CRS. In principlea base station may be configured to transmit CRS at higher power toincrease the likelihood of successful reception by terminal devices inpoor coverage areas. However, in practice this may causeinteroperability issues for older conventional terminal devices whichmight be operating in the wireless telecommunication system and whichare expecting to see conventional CRS signals. In other examples,synchronization signalling, for example conventional LTE primary orsecondary synchronisation signalling (PSS/SSS), may be treated asreference signals for the purpose of measuring channel conditions inrespect of received signal strength.

In still other examples, a new type of reference signal may be definedfor the purpose of establishing whether terminal devices require powerboosting. For the sake of convenience this may be referred to here aspower boost reference signals/signalling. The characteristics of powerboost reference signals might be configured so as to increase thelikelihood of reliable reception by terminal devices in poor coverageareas (i.e. the areas where the virtual carrier power boosting inaccordance with an embodiment of the invention is likely to bebeneficial).

Thus, power boost reference signalling may, for example, be transmittedin subframes in which a base station is transmitting a power boostedvirtual carrier. In this regard, the reference signalling might readilybe transmitted with increased power (relative to non-power boostedtransmissions in the wireless telecommunications system) to improve thelikelihood of reliable detection. In this regard the power boostreference signalling may be transmitted with a higher power than, forexample, cell specific reference signals (CRS). The power boostedreference signals may be positioned within the subframe with apredefined timing offset relative to synchronisation signals, therebyallowing terminal devices to readily monitor the appropriate timing inthe subframe to seek to detect the power boost reference symbol.Furthermore, power boost reference signalling may be transmitted onfrequencies within the virtual carrier frequency bandwidth. However, inother cases the power boost reference signalling may be transmittedelsewhere, for example on host-carrier frequencies. In any event, it maybe helpful for power boost reference signalling to be transmitted onpre-defined frequencies to aid detection by terminal devices. It may beexpected that terminal devices for which virtual carrier operation isappropriate might frequently be deployed with relatively low mobility.In this case, power boost reference signalling may be less frequent thanconventional reference signalling, such as CRS. Furthermore, because theterminal devices for which virtual carrier operation is appropriatemight frequently be associated with delay-tolerant communications, powerboost reference signalling may be transmitted in a discontinuous manner.For example, power boost reference signalling may be transmitted for 1minute every 15 min, or according to some other duty cycle according tothe implementation at hand. Similarly, in some implementations virtualcarrier power boosting might be applied only during periods of lownetwork activity, for example during what might be termed quite times,such as during the night or early hours of the morning. In this case,power boost reference signalling might correspondingly be transmittedonly during those times when virtual carrier power boosting may beactive.

In situations where penetration loss between a base station and aterminal device is particular the high, conventional-type L1 CQI reportsignalling may not have sufficient gain to compensate for the past loss.In order to address this, conventional uplink coverage improvementtechniques, for example those based on repetition, bundling and/orcoding gain, may be applied in respect of a terminal device's CQI reportsignalling.

Such CQI reporting might follow the generally established techniques,but with a border range of potential reported values to accommodate thesituation of a terminal device reporting that it is in an area wherevirtual carrier power boosting may be beneficial. For example,conventional CQI reporting may be based around a value range of 0-15.The CQI reporting value zero indicates a terminal device is out ofcoverage. A terminal device which may require virtual carrier powerboosting may thus be configured to report CQI values over an extendedrange. For example, the addition of a single bit to indicate negativevalues may be used to allow a terminal device to in effect extend theavailable range of CQI values to −15 to +15, with negative valuesindicating the terminal device requires power boosting.

As noted above, an alternative approach for identifying terminal devicesas potentially benefiting from power boosted virtual carrier operationmay be based on past loss measurements. Reference signal received power(RSRP) is an existing concept in LTE-type wireless telecommunicationssystems and is defined as the linear average over the powercontributions of the resource elements that carry cell-specificreference signals within a considered measurement frequency bandwidth.RSRP is the basic measurement for conventional pathloss calculations.

An approach based around existing path loss calculation schemes isschematically represented in the signalling ladder diagram of FIG. 21.FIG. 21 represents signalling in accordance with an embodiment of theinvention between an MTC type terminal device 1403A and a base station1401A, for example of the kind represented in FIG. 14. Working from thetop down, in a first step the base station 1401A determines a referencesignal to be transmitted. In a second step the base station 1401Atransmits the reference signal, and it is received by the terminaldevice 1403A. From the received reference signal the terminal device1403A establishes a RSRP measurement. This may be performed inaccordance with generally conventional RSRP measurement techniques forthe reference signal received. As for the above-described examples basedon CQI reporting, the reference signalling employed in the example ofFIG. 21 might be CRS or alternative reference signalling such as for theexamples discussed above.

To determine pathloss from RSRP a terminal device needs an indication ofthe power which with which the reference signal was transmitted. Thus,the base station is configured to transmit system information regardingthe transmission power for the reference signalling, as schematicallyindicated in FIG. 21 in the two stages following the RSRP measurement bythe terminal device. If the reference signal is transmitted by the basestation with increased power in power boosted virtual carrier subframesrelative to its transmissions in non-power boosted virtual carriersubframes (to be received by conventional terminal devices), the basestation may also communicate an indication of this offset. That is tosay, the base station's indication of the transmitted signal strengthmay correspond with an indication of the reference signallingtransmission strength in non-power boosted subframes along with anindication of an additional power offset associated with power boostedsubframes. Thus, the terminal device can establish the transmissionpower associated with the reference signal for which the RSRPmeasurement is made, and determine the path loss in accordance withgenerally conventional techniques. In a final step of the processschematically represented in FIG. 21, the terminal device 1403Atransmits a pathloss (or RSRP) report to the base station 1401A. Thismay again be performed in accordance with generally conventional RSRPreporting techniques in LTE-type wireless telecommunications systems.Having received the pathloss/RSRP report, the base station may determinefrom the reported power/pathloss received by the terminal device whetheror not the terminal device is in a location which would benefit fromvirtual carrier power boosting. In an alternate approach there may be nobroadcasting of transmission power boost information by the basestation. In this case, the terminal device may send an RSRP report inthe normal way, and the base station may then calculate an actualpathloss based on its own knowledge of the transmission power for thereference signal on which the terminal device's report is based.

Yet another example mechanism for establishing whether a terminal deviceis one which would benefit from virtual carrier power boosted operationmay be referred to as a paging-based approach. An example of thisapproach is schematically represented in the signalling ladder diagramof FIG. 22. FIG. 22 represents signalling in accordance with anembodiment of the invention between an MTC type terminal device 1403A, abase station 1401A, and a core network 1408, for example of the kindrepresented in FIG. 14.

Working from the top down in FIG. 22, in a first step an MME element ofthe core network 1408 initiates a paging procedure by sending a pagingrequest to the base station associated with the MTC terminal device1403A. On receiving the paging request from the core network element1408, the base station 1401A initiates terminal device paging inaccordance with an embodiment of the invention. In a broad summary, thetechnique involves the base station sending a sequence of pagingmessages with increasing gain until a response is received from theterminal device.

Thus, referring again to the signalling represented in FIG. 22, the basestation first sends to the terminal device a conventional-type pagingmessage with a first transmission power, referred to in FIG. 22 as level1 paging. If no response is received from the terminal device, as in theexample represented in FIG. 22, the base station is configured to send asecond conventional-type paging message having a higher power, referredto in FIG. 22 as level 2 paging. The base station may repeatedly sendpaging messages with increasing gain (e.g. increasing power) until anappropriate response from the terminal device is received, for example aresponse of the type conventionally expected in response to a pagingmessage. In the example of FIG. 22 it is assumed the second level pagingmessage (MTC paging level 2) has sufficient transmission power to bereceived by the terminal device, and so the terminal device provides anappropriate response, for example on a random access channel.

On receiving the response, the base station can allocate the terminaldevice a temporary ID, e.g. a cell radio network temporary identifier(C-RNTI) in accordance with broadly conventional paging techniques, andcommunicate this to the MTC terminal device. Furthermore, based on thetransmission power of the paging signal to which the terminal deviceresponded, the base station can establish whether or not the terminaldevice is in a location associated with a penetration loss which wouldmean power boosting would be advantageous.

In order to extend the paging channel coverage, various techniques maybe applied. In current LTE systems the paging signalling is transmittedby PDCCH. One simple way of implementing the above-described multi-levelpaging technique would be sequentially increasing the power of PDCCHtransmissions. For example, a power offset from an original (baseline)power maybe adopted in a series of steps (e.g. 0, 3, 6 dB).

In some examples there may not be sufficient headroom available for thebase station to increased power in this way. In this case, othertechniques for in effect obtaining transmission gain of the pagingchannel may be adopted. Such techniques include, for example,beamforming gain, soft combining gain, and repetition/channel codinggain.

Beamforming gain may be provided with paging signalling by E-PDCCH(Enhanced Physical Downlink Control Channel) instead of PDCCH. E-DPCCHsupports beamforming, which is useful for coverage extension becausethere is beamforming gain (direction gain). In some circumstances it maybe inappropriate to use a beamforming gain approach for the pagingchannel because of terminal device mobility meaning the base station maynot be fully aware of the position of the terminal device before paging.However, for the MTC-type terminal devices with low mobility, forexample because they are installed at a fixed location, this will not bean issue.

For a soft combining gain approach paging may use a MBSFN supportchannel such as PMCH (Physical Multicast Channel). In accordance withthis approach a new paging channel may be introduced into the MBSFNsubframe to allow the transmission of a paging signal simultaneouslyamong cells by using soft combining (coherent receiving). MBSFN isrelatively simple to adopt in a SFN (single frequency network) anddifferent delays from multiple cells can be accommodated by using a longCP (cyclic prefix)

For a repetition/channel coding gain approach there may be paging by thesame channel as for current paging (PDCCH), but the functionality may beextended for additional gain. For example, in PDCCH coverage depends onthe CCE (Control Channel Element) aggregation level. One way to increasegain is for the CCE aggregation level to be extended beyond the currentmaximum value (e.g. the current maximum CCE aggregation size is 8, so,for example a maximum CCE size of 12 or 16, could be used instead). Analternate way is to provide for some data repetition, for examplerepeating paging over more than 1 sub frame.

Thus, to summarise multi-level MTC paging approaches of the kindschematically represented in FIG. 22, multiple levels of paging areintroduced to help the base station determining a path loss level (basedon what level of paging is eventually received by the terminal device).A first level (paging level 1) may correspond with a conventional pagingmessage with no additional gain. This might correspond with the paginglevel expected to be appropriate for a conventional LTE device, forexample. A second level (paging level 2) might be associated with afirst step increase in gain (e.g. by power boosting transmissions by 3dB, providing for repetition over 2 subframes, or increasing to 12 thenumber of CCEs for aggregation). A third level (paging level 3) might beassociated with a further step increase in gain (e.g. by power boostingtransmissions by 6 dB, providing for repetition over 3 subframes, orincreasing to 16 the number of CCEs).

As noted above, a significant aspects of certain embodiments of theinvention is that base stations in a wireless telecommunications systemmay exchange signalling messages relating to their intended adoption ofpotential enhanced/increased power transmissions on frequenciesassociated with a virtual carrier as compared to other frequenciestransmitted by the base station. A convenient interface for supportingsuch inter-base station communications in a LTE-type system is theestablished X2 interface provided for inter-base station communications.However, it will nonetheless be appreciated that in accordance withother embodiments, other techniques for supporting inter-base thatsignalling may be provided.

As explained above, conventional LTE networks may support the softfrequency reuse ICIC technique. In accordance with this technique thereis defined the Relative Narrowband Transmit Power (RNTP) informationelement (IE) which may be exchanged using X2 signalling along with anRNTP threshold IE in a so-called load information message. ConventionalRNTP signalling comprises a series of bits corresponding with respectiveresource blocks (RBs) of a wireless telecommunications system bandwidth.The base station communicating RNTP signalling to a neighbouring basestation over at the X2 interface sets the respective bits of the RNTP IEto indicate whether or not the corresponding resource block might betransmitted by the base station in the upcoming period (i.e. the periodfor which the RNTP signalling remains valid) with a power which exceedsthe threshold power defined in the RNTP threshold IE. Furtherinformation regarding conventional RNTP signalling can be found in therelevant standards. Example, see 3GPP TS 36.423 version 11.2.0 (Release11) [16]. In accordance with certain embodiments of the invention anadapted form of RNTP may be adopted as a format with which base stationscoordinate their intended power boosted virtual carrier transmissions.

Thus, in one example base stations operating in accordance withembodiments of the invention may communicate information regarding theirintended use of power boosted virtual carrier transmissions (for examplein association with steps S4 and S10 of FIG. 18) by exchangingsignalling similar to existing RNTP signalling. During power boosting abase station can adopt significantly different power transmissions fordifferent OFDM subcarriers depending on whether the respectivesubcarriers are inside or outside the virtual carrier bandwidth.Accordingly, it may be appropriate for different RNTP thresholds to beset for virtual carrier and non-virtual carrier transmissions. Thus, inaccordance with certain embodiments of the invention, a new informationelement may be defined for X2 signalling to identify a differentthreshold for virtual carrier power boosted transmissions. Thisinformation may be conveniently referred to here as a power boostRelative Narrowband Transmit Power threshold IE.

In current LTE-type systems the RNTP threshold can adopt a value asfollows:RNTP_(threshold)∈{−∞,−11,−10,−9,−8,−7,−6,−5,−4,−3,−2,−1,0,+1,+2,+3} dB.However, it is expected that for some virtual carrier power boostingimplementations in accordance with embodiments of the inventionsignificantly higher transmission powers may be desired, for example upto 20 dB. Thus, correspondingly higher values may be defined for theproposed power boost RNTP threshold information element in accordancewith some embodiments of the invention. In some examples a wirelesstelecommunications system may be configured such that power boosting issimply on or off with no variation in power. In this case, there may bea reduced number of potential values for power boost RNTP threshold. Forexample only three values might be available with a value +X dBcorresponding with power boosting by an amount X (where X will depend onhow much power boosting the system allows, for example X might be 20), avalue of zero dB corresponding with no power boosting applied on thevirtual carrier, and a value of −∞ being used if there are no virtualcarrier transmissions for the upcoming period.

In some example embodiments there may be no need for a specific RNTPthreshold information element to be communicated between base stations,for example where power boosting is either on or off and applied at apredefined level. In this case the inter-base station to locations maysimply comprise a bit string in which the different bits related todifferent frequencies that may be adopted for virtual carriertransmissions, and a value of zero or one is selected to indicatewhether or not transmissions on the corresponding frequencies are to bepower boosted or not. In some examples such a bit string may follow theconventional RNTP approach of associating different bits with differentresource blocks. However, in many cases it may be the case that powerboosting is to be applied it will be applied to all the resource blockcomprising a virtual carrier. Thus, in some examples where there mightbe a predefined number of virtual carriers, the bit string may simplycomprise a single bit for each virtual carrier. For example if awireless telecommunications system supports a fixed number of fourvirtual carriers with the respective virtual carriers being identifiedby corresponding index values 0, 1, 2, 3, the bit string may simplycomprise four bits. A bit value of 0 or 1 may thus be used to indicatewhether transmissions from the base station on the corresponding virtualcarrier are to support power boosted operation in the upcoming period.For example, a power boost RNTP message comprising the bit string [0010]may be taken to comprise an indication that the base station intends toapply power boosting to the third virtual carrier supported in thewireless telecommunications system.

It will be appreciated similar bit string approach can be taken toidentify time periods in which a base station intends to adopt powerboosted operation in cases where power boosting may be applied on a persubframe basis over a coordination period. For example, if acoordination period comprises 40 subframes, a 40 bit message may be sentby a base station to neighbouring base stations to indicate which ofthose 40 subframes are intended to be used for power boosted by the basestation sending the message.

It will be appreciated that various modifications can be made to theembodiments described above without departing from the scope of thepresent invention as defined in the appended claims.

For example, in some implementations a base station may be configured toalways apply power boosting for all its virtual carrier transmissions.In this case an operating step corresponding to step S2 in FIG. 18 wouldsimply rely on the base station determining whether there are anyvirtual carrier transmissions to be made at all for an upcoming period,regardless of the destination terminal device, i.e. regardless ofwhether it is in a poor coverage location require power boosting forreliable transmissions.

In some implementations base stations may coordinate in accordance withthe principles described above to exchange information regarding thetransmission resources on which they intend to adopt virtual carriertransmissions, for example in terms of time and/or frequency, withoutspecifically indicating whether or not those transmissions will be powerboosted. The respective base stations may then select their owntransmission resources to be used for virtual carrier transmissions in amanner which avoids overlap with neighbouring base stations inaccordance with the principles described above. Thus, in accordance withthis approach the respective base stations are configured to help avoidthe situation in which neighbouring base stations are employing the sameresources for their virtual carrier transmissions. The individual basestations may then be free to apply power boosting as desired on thevirtual carrier on the understanding there will be no neighbouring basestations using the same virtual carrier resources. That is to say, thecharacteristics regarding a base station's upcoming virtual carriertransmissions that are communicated to neighbouring base stations inaccordance with embodiments of the invention may simply comprise anindication of the transmission resources to be used by the base stationto support virtual carrier transmissions without any indication ofwhether or not power boosting is to be adopted.

Furthermore, although embodiments of the invention have been describedwith reference to an LTE mobile radio network, it will be appreciatedthat the present invention can be applied to other forms of network suchas GSM, 3G/UMTS, CDMA2000, etc. The term MTC terminal as used herein canbe replaced with user equipment (UE), mobile communications device,terminal device etc. Furthermore, although the term base station hasbeen used interchangeably with eNodeB it should be understood that thereis no difference in functionality between these network entities.

The above-described implementations of a power-boosted virtual carrierin wireless telecommunications systems according to embodiments of theinvention provide schemes for improved communication reliability ondownlink through transmission power budget concentration within arelatively narrow-band virtual carrier within a host carrier spanning awider system bandwidth. It will be appreciated that in somecircumstances it may be necessary for a terminal device requiring powerboosted virtual carrier transmissions to reliably receive informationfrom a base station may need to take steps to improve reliability of itsuplink transmissions. There are various ways this can be done. Forexample, a brute force approach may be to simply provide the terminaldevice with a more powerful transmitter by separate power amplifier toovercome the additional path losses associated with its transmissions.For example, a terminal device in a basement having an additionalattenuation of n dB as compared to a nearby terminal device outside thebasement may be provided with a transmitter configured to transmit withsufficient power to overcome the additional n dB loss. Other techniquesmight involve adopting established approaches for extending uplinkcoverage in wireless telecommunications systems. For example, oneapproach in respect of RACH transmissions would be for a base station toindicate to a terminal device identified as one potentially requiringpower boosted transmissions that it should adopt a large repetition RACHformat, such as the defined preamble formats 3 or 4 in LTE-basedwireless communications systems. An approach in respect of PUSCH (uplinkdata channel) communications might be to adopt known techniques such asTTI bundling to increase the reliability of success for uplinktransmission from the terminal device to the base station. Thus, Amethod of operating a base station in a wireless telecommunicationssystem has been described. Downlink communications from the base stationto terminal devices are made using a plurality of OFDM sub-carriersspanning a system frequency bandwidth. The base station supportscommunications with a first type of terminal device on a host carrierusing OFDM sub-carriers distributed across the system frequencybandwidth and supports communications with a second type of terminaldevice on a restricted bandwidth carrier using OFDM sub-carriersdistributed across a restricted frequency bandwidth which is smallerthan and within the system frequency bandwidth. The base stationreceives from a further base station of the wireless telecommunicationssystem an indication of a transmission characteristic to be used by thefurther base station for transmissions to the second type of terminaldevice using a reduced bandwidth carrier associated with the furtherbase station. The base station selects a transmission characteristic forits own transmissions to be made to the second type of terminal deviceusing the restricted bandwidth carrier in a manner that takes account ofthe indication of the transmission characteristic received from thefurther base station. The base station then conveys an indication of thetransmission characteristic from the base station to at least one otherbase station of the wireless telecommunications system. Thus, therespective base stations exchange information regarding their restrictedbandwidth carrier transmissions to help them coordinate their respectivetransmissions with a view to reducing intercell interference.

Further particular and preferred aspects of the present invention areset out in the accompanying independent and dependent claims. It will beappreciated that features of the dependent claims may be combined withfeatures of the independent claims in combinations other than thoseexplicitly set out in the claims.

REFERENCES

-   [1] ETSI TS 122 368 V10.530 (2011 July)/3GPP TS 22.368 version    10.5.0 (Release 10)-   [2] UK patent application GB 1101970.0-   [3] UK patent application GB 1101981.7-   [4] UK patent application GB 1101966.8-   [5] UK patent application GB 1101983.3-   [6] UK patent application GB 1101853.8-   [7] UK patent application GB 1101982.5-   [8] UK patent application GB 1101980.9-   [9] UK patent application GB 1101972.6-   [10] UK patent application GB 1121767.6-   [11] UK patent application GB 1121766.8-   [12] Holma H. and Toskala A, “LTE for UMTS OFDMA and SC-FDMA based    radio access”, John Wiley and Sons, 2009-   [13] Nomor Research GmbH—“Heterogeneous LTE Networks and Intercell    Interference Coordination”, Pauli et al.-   [14] ZTE Corporation—“Enhanced ICIC for LTE-A HetNet”, Xiong.-   [15] ETSI TS 136 420 V11.0.0 (2012 October)/3GPP TS 36.420 version    11.0.0 (Release 11)-   [16] 3GPP TS 36.423 version 11.2.0 (Release 11)

1. A method of operating a base station in a wireless telecommunicationssystem in which downlink communications from the base station toterminal devices are made using a plurality of Orthogonal FrequencyDivision Multiplex, OFDM, sub-carriers spanning a system frequencybandwidth, and wherein the base station supports communications with afirst type of terminal device on a host carrier using OFDM sub-carriersdistributed across the system frequency bandwidth and supportscommunications with a second type of terminal device on a restrictedbandwidth carrier using OFDM sub-carriers distributed across arestricted frequency bandwidth, wherein the restricted frequencybandwidth is smaller than and within the system frequency bandwidth, andwherein the method comprises: receiving from a further base station ofthe wireless telecommunications system an indication of a transmissioncharacteristic to be used by the further base station for transmissionsto the second type of terminal device using a reduced bandwidth carrierassociated with the further base station; and selecting a transmissioncharacteristic for transmissions to be made by the base station to thesecond type of terminal device using the restricted bandwidth carrier ina manner that takes account of the indication of the transmissioncharacteristic received from the further base station.
 2. A base stationin a wireless telecommunications system in which downlink communicationsfrom the base station to terminal devices are made using a plurality ofOrthogonal Frequency Division Multiplex, OFDM, sub-carriers spanning asystem frequency bandwidth, and wherein the base station supportscommunications with a first type of terminal device on a host carrierusing OFDM sub-carriers distributed across the system frequencybandwidth and supports communications with a second type of terminaldevice on a restricted bandwidth carrier using OFDM sub-carriersdistributed across a restricted frequency bandwidth, wherein therestricted frequency bandwidth is smaller than and within the systemfrequency bandwidth, and wherein the base station is configured toreceive from a further base station of the wireless telecommunicationssystem an indication of a transmission characteristic to be used by thefurther base station for transmissions to the second type of terminaldevice using a reduced bandwidth carrier associated with the furtherbase station; and to select a transmission characteristic fortransmissions to be made by the base station to the second type ofterminal device using the restricted bandwidth carrier in a manner thattakes account of the indication of the transmission characteristicreceived from the further base station.
 3. The base station according toclaim 2, wherein the transmission characteristic associated with theindication received from the further base station comprises frequencyand/or time resources on which transmissions are to be made by thefurther base station to the second type of terminal device using arestricted bandwidth carrier.
 4. A base station according to claim 2,wherein the transmission characteristic associated with the indicationreceived from the further base station comprises an identifier for arange of frequencies for the restricted bandwidth carrier selected froma set of potential ranges of frequencies for restricted bandwidthcarriers that are supported in the wireless telecommunications system.5. The base station according to claim 2, wherein the transmissioncharacteristic associated with the indication received from the furtherbase station comprises an indication of physical resource blocks to beused by the further base station for transmitting a restricted bandwidthcarrier.
 6. The base station according to claim 2, wherein the wirelesstelecommunications system uses a radio frame structure comprisingsubframes, and wherein the base station is configured such that theindication of the transmission characteristic received from the furtherbase station comprises an indication of one or more subframes to be usedby the further base station for transmissions to the second type ofterminal device using a restricted bandwidth carrier.
 7. The basestation according to claim 2, configured such that the indicationreceived from the further base station comprises an indication thattransmissions are to be made by the further base station to the secondtype of terminal device using a restricted bandwidth carrier with amaximum transmission power threshold which is greater than a maximumtransmission power threshold for contemporaneous transmissions to bemade by the further base station to the first type of terminal device.8. The base station according to claim 2, configured such that thetransmission characteristic selected by the base station fortransmissions to be made to the second type of terminal device using therestricted bandwidth carrier comprises frequency and/or time resourceson which the transmissions are to be made by the base station to thesecond type of terminal device using the restricted bandwidth carrier.9. The base station according to claim 2, configured such that theindication of a transmission characteristic received from the furtherbase station comprises an indication of frequency and/or time resourceson which transmissions are to be made by the further base station to thesecond type of terminal device using a restricted bandwidth carrierassociated with the further base station, and wherein the base stationis configured to select a transmission characteristic for transmissionsto be made by the base station to the second type of terminal deviceusing the restricted bandwidth carrier by selecting frequency and/ortime resources to be used for the restricted bandwidth carrier which aredifferent from the frequency and/or time resources comprising theindication of a transmission characteristic received from the furtherbase station.
 10. The base station according to claim 2, furtherconfigured to convey an indication of the transmission characteristicselected by the base station for transmissions to be made by the basestation to the second type of terminal device using the restrictedbandwidth carrier to at least one other base station of the wirelesstelecommunications system.
 11. The base station according to claim 10,wherein the further base station from which an indication of frequencyand/or time resources on which transmissions are to be made by thefurther base station is received is one of the at least one other basestation to which the base station conveys an indication of the selectedtransmission characteristic.
 12. The base station according to claim 2,further configured to make transmissions to the second type of terminaldevice in accordance with the selected transmission characteristic usingthe restricted bandwidth carrier with a maximum transmission powerthreshold which is greater than a maximum transmission power thresholdfor contemporaneous transmissions made by the base station to the firsttype of terminal device using the host carrier.
 13. The base stationaccording to claim 2, further configured to make transmissions to thesecond type of terminal device in accordance with the selectedtransmission characteristic using the restricted bandwidth carrier witha transmission power which is greater than a maximum transmission powerthreshold for contemporaneous transmissions made by the base station tothe first type of terminal device using the host carrier.
 14. The basestation according to claim 2, configured such that the indication of thetransmission characteristic is received from the further base stationover a point-to-point logical interface between the base station and thefurther base station.
 15. The base station according to claim 14,configured such that the indication of the transmission characteristicis received from the further base station over an X2 interface of thewireless telecommunications system.
 16. The base station according toclaim 15, configured such that the indication of the transmissioncharacteristic is received from the further base station in aninformation element defined for the X2 interface.
 17. The base stationaccording to claim 2, wherein the first type of terminal device and thesecond type of terminal device are types of terminal device havingdifferent operating capabilities.